TreeGov — Risk Segmentation Workbench

Version: 1.0.0rc4 Author: Marco Rengel License: Apache 2.0 Graphics engine: PySide6 Analytical engine: Python (NumPy, pandas, scipy.stats) Test suite: 438/438 passing

⚠️ Regulatory notice. TreeGov is under technical validation (Model Risk Management - MRM). Restricted use: technical MRM validation. Not fit for banking production without regulatory approval. Any use in a regulated production environment (banking or otherwise) requires independent validation, formal approval, and integration with the institution's model governance framework.

Data scope. TreeGov is developed exclusively with public datasets (German Credit, UCI) and synthetic data. It is designed for end use with real banking data on the analyst's desktop: the CSV never leaves the machine. No real data is sent to third-party AI APIs during development. When TreeGov is used in production with real data, the DEBUG logs and exported HTML reports contain sensitive model information (per-node PDs, segment counts, real column names, file paths) and should be treated as confidential material by the analyst.

Executive summary

TreeGov is an open-source platform to build, validate, and audit decision-tree models in regulated environments. It is the successor to classic GUI tools (now discontinued) that allowed analysts to build models without programming. Unlike closed corporate suites, TreeGov democratizes model governance (MRM) and compliance with standards such as Basel and IFRS 9.

The system implements CHAID (classic and Exhaustive), C&RT, and QUEST with white-box mathematics: every statistical formula is written explicitly and cited to its original publication. Governance is opt-out through two explicit modes. Regulatory mode (the default) applies the full MRM layer required by banks and credit bureaus: Jeffreys estimator, PD floor (BCBS CRE 20.39), and fingerprints that record the choice. Research mode produces raw empirical probabilities, opening the tool to domains such as health, biology, or social sciences. The choice is always explicit and never silent.

Traditional libraries (scikit-learn, statsmodels, or R packages) require writing code, which takes time away from analysis. Meanwhile, the visual tools that existed in the past were discontinued. TreeGov fills that void by combining an open-source visual environment with regulatory traceability (SR 11-7, Basel, IFRS 9) as a core design principle.

Philosophy

“Python gives you the engine. TreeGov gives you the engine, the brakes, the dashboard, the seatbelt, and the maintenance log. Which would you choose for a model that will be audited by the regulator?”

TreeGov starts from one premise: model governance is not a layer you add at the end, but a principle woven into every component. While statistical libraries and scripting environments provide the analytical engine, TreeGov provides in addition the brakes (MRM controls), the dashboard (graphical display), the seatbelt (auditability), and the maintenance log (the immutable audit trail). For a model that will be audited by a regulator, the choice is not technical: it is about governance.

Beyond using MRM inside the tool, the software itself is built under MRM discipline: design audits before code, human-in-the-loop supervision, adversarial verification, and immutable traceability for every release.

Read the full project philosophy → English · Español

flowchart TB
    TG["<b>🌳 TreeGov</b><br/>Risk Segmentation Workbench<br/><i>by Marco Rengel</i>"]

    TG --> P["<b>🎯 Purpose</b><br/>Risk segmentation<br/>with MRM/IFRS 9 governance"]
    TG --> M["<b>🧮 Engines</b><br/>CHAID · C&RT · QUEST<br/>White box + citations"]
    TG --> G["<b>🔒 Governance</b><br/>SplitConfig frozen<br/>Fingerprint sha256<br/>Audit log"]
    TG --> S["<b>🛠️ Stack</b><br/>Python 3.11 · PySide6<br/>numpy · pandas · scipy<br/>Apache 2.0"]

    P --> ARQ["<b>🏗️ Architecture</b><br/>Strict clean room"]
    M --> ARQ
    G --> ARQ
    S --> ARQ

    ARQ --> BE["<b>backend_v3</b><br/>Analytical layer<br/>zero Qt imports"]
    ARQ --> FE["<b>frontend_v3</b><br/>Presentation layer<br/>zero numpy imports"]

    BE -.->|Session| FE

    ARQ --> ST["<b>📊 Current status</b><br/>✅ Phases 0 → 3.9 complete<br/>📦 v1.0.0rc4 published on PyPI<br/>🧪 435 / 435 tests PASSED<br/>📅 Oct 20, 2026"]

    style TG fill:#0D47A1,color:#fff,stroke:#002171,stroke-width:2px
    style P fill:#2E7D32,color:#fff
    style M fill:#2E7D32,color:#fff
    style G fill:#2E7D32,color:#fff
    style S fill:#2E7D32,color:#fff
    style ARQ fill:#E65100,color:#fff
    style BE fill:#37474F,color:#fff
    style FE fill:#37474F,color:#fff
    style ST fill:#1565C0,color:#fff

What is TreeGov?

TreeGov is an analytical workbench to build, evaluate, and audit decision trees in regulated environments. Unlike machine learning libraries, where the analyst operates in a black box, TreeGov provides a visual environment with explicit mathematics and absolute traceability.

The core feature of TreeGov is radical auditability. Absolutely every stage of the model's lifecycle can be traced by an auditor:

• The code: every statistical formula is written explicitly and cited to its original publication.
• The decisions: the architecture and trade-offs are documented to justify every choice.
• The model: every training run generates a unique fingerprint that acts as an immutable seal.
• The evidence: a transactional log records every step, and a suite of over 400 tests (including validated public datasets) guarantees reproducibility.

Design principles

1. Clean-room architecture: strict separation between the analytical backend (backend_v3/, no GUI dependencies) and the presentation layer (frontend_v3/, no analytical logic).
2. White box: sklearn, statsmodels, and any other black-box library are forbidden. Every statistical formula is written explicitly in the code, with its bibliographic citation.
3. Native governance: DEBUG-grade transactional logging, immutable configuration (SplitConfig frozen), and mathematical invariant validation at construction time.

Analytical capabilities

Technology stack

• Python 3.11 / 3.12
• PySide6 (graphical interface)
• numpy, pandas, scipy.stats (statistical computation)
• pyarrow, openpyxl (data ingestion)
• pytest (optional: tests are runnable with plain python)

Repository structure

TreeGov/
├── backend_v3/              # Pure analytical layer (0 Qt imports)
│   ├── import_guard.py      # Black-box library blocker
│   ├── log_config.py        # DEBUG transactional logger
│   ├── types.py             # SplitConfig (frozen) + enums
│   ├── statistics.py        # chi2, F, Brown-Forsythe, Stirling, Kass
│   ├── imputation.py        # TrainOnlyImputer (anti-leakage)
│   ├── chaid_engine.py      # CHAID classic + Exhaustive
│   ├── crt_engine.py        # C&RT multiclass + surrogate splits
│   ├── quest_engine.py      # QUEST multiclass + QDA/Gini
│   ├── splitting.py         # Hamilton-Hare stratified split
│   ├── profiling.py         # Predictor type inference
│   ├── tree_builder.py      # BFS tree construction + TreeModel
│   ├── session_state.py     # Flow state machine (EMPTY to TRAINED to OOT)
│   ├── validation.py        # OOS metrics + OOT evaluation
│   ├── pruning.py           # Cost-complexity pruning (Breiman)
│   ├── reporting.py         # Gains table + classification matrix DTOs
│   └── stability.py         # PSI / CSI / Gini Drop
├── frontend_v3/             # Presentation layer (Phase 2)
├── tests/                   # Unit tests (dual: pytest / python direct)
├── docs/                    # Documentation
│   ├── methodology.md       # Mathematical methodology (EN)
│   ├── design_decisions.md  # Implementation decisions (EN)
│   ├── 3.1_design_multiclass.md  # Phase 3.1 design (EN)
│   ├── 3.2_decisions_consolidated.md  # Phase 3.2 decisions (EN)
│   ├── 3.3_design_population_categories.md  # Phase 3.3 design (EN)
│   ├── 3.4_design_multiclass_crt_quest.md  # Phase 3.4 design (EN)
│   ├── 3.5_design_multiclass_weighted_reports.md  # Phase 3.5 design (EN)
│   ├── 3.6_design_public_datasets.md  # Phase 3.6 design (EN)
│   ├── validation_results_3.6.md  # UCI validation report (EN)
│   ├── security_audit.md      # Security and privacy audit (EN)
│   ├── api.md               # Public API (EN)
│   ├── roadmap.md           # Phase plan (EN)
│   ├── philosophy.md        # Project philosophy (EN)
│   ├── philosophy.es.md     # Philosophy (ES)
│   ├── estado_proyecto.md   # Project state dossier (ES)
│   ├── audit_log.md         # Audit trail (ES)
│   ├── contexto_para_nueva_sesion.md  # Session bootstrap (ES)
│   └── prompt_para_asistente.md       # Assistant brief (ES)
├── archive/                 # Historical documents (read-only)
├── data/                    # Datasets (read-only, Git-ignored)
├── logs/                    # Per-run execution logs (Git-ignored)
├── treegov.py               # Headless orchestrator (CLI)
├── treegov_gui.py           # GUI entry point (Phase 2)
├── pyproject.toml           # Packaging
├── requirements.txt         # Working minimum pins (pyproject.toml is source of truth)
├── opencode.json            # OpenCode project configuration
├── README.md                # This file (EN)
├── README.es.md             # Spanish translation
├── AGENTS.md                # Operating instructions for AI agents
├── CONVENTIONS.md           # Operational conventions for Aider
├── LICENSE                  # Apache 2.0
├── NOTICE.md                # Legal notice and attribution
├── .gitignore               # Git exclusions
├── .aiderignore             # Aider repo-map exclusions
├── .gitattributes           # Line-ending normalization
├── .aider.conf.example.yml  # Aider configuration template
└── .treegovrules            # Governance rules for AI agents

Why TreeGov?

Quick start

Installation

.\.venv\Scripts\python -m pip install -r requirements.txt

Headless demo (Phase 0)

.\.venv\Scripts\python treegov.py

Performance benchmark (N=1M)

.\.venv\Scripts\python tests\benchmark_1m.py --n 1000000 --seed 42

Test suite

.\.venv\Scripts\python -m pytest tests -q

Project status

Test suite: 438/438 passing.

Academic references

• Biggs, D., de Ville, B. & Suen, E. (1991). A Method of Choosing Multiway Partitions for Classification and Decision Trees. Journal of Applied Statistics 18(1), 49-62.
• Breiman, L., Friedman, J.H., Olshen, R.A. & Stone, C.J. (1984). Classification and Regression Trees. Wadsworth.
• Brier, G.W. (1950). Verification of forecasts expressed in terms of probability. Monthly Weather Review 78(1), 1-3.
• Brown, M.B. & Forsythe, A.B. (1974). Robust Tests for the Equality of Variances. Journal of the American Statistical Association 69(346), 364-367.
• Cochran, W.G. (1954). Some Methods for Strengthening the Common Chi-2 Tests. Biometrics 10(4), 417-451.
• Davis, J. & Goadrich, M. (2006). The relationship between Precision-Recall and ROC curves. Proceedings of the 23rd International Conference on Machine Learning (ICML), 233-240.
• Fagerland, M.W., Hosmer, D.W. & Bofin, A.M. (2012). Multinomial goodness-of-fit tests for logistic regression models. Statistics in Medicine, 31(30), 4238-4253.
• Fisher, R.A. (1925). Statistical Methods for Research Workers. Oliver & Boyd, Edinburgh.
• Hanley, J.A. & McNeil, B.J. (1982). The meaning and use of the area under a receiver operating characteristic (ROC) curve. Radiology 143(1), 29-36.
• Hand, D.J. & Till, R.J. (2001). A simple generalisation of the area under the ROC curve for multiple class classification problems. Machine Learning, 45(2), 171-186.
• Heeringa, S.G., West, B.T. & Berglund, P.A. (2010). Applied Survey Data Analysis. Chapman & Hall/CRC.
• Hosmer, D.W. & Lemeshow, S. (1980). A goodness-of-fit test for the multiple logistic regression model. Communications in Statistics A10, 1043-1069.
• Jeffreys, H. (1946). An invariant form for the prior probability in estimation problems. Proceedings of the Royal Society of London A 186(1007), 453-461.
• Kass, G.V. (1980). An Exploratory Technique for Investigating Large Quantities of Categorical Data. Applied Statistics 29(2), 119-127.
• Levene, H. (1960). Robust tests for equality of variances. In Contributions to Probability and Statistics, Stanford University Press, 278-292.
• Loh, W.-Y. & Shih, Y.-S. (1997). Split Selection Methods for Classification Trees. Statistica Sinica 7(4), 815-840.
• Pearson, K. (1900). On the criterion that a given system of deviations from the probable in the case of a correlated system of variables is such that it can be reasonably supposed to have arisen from random sampling. Philosophical Magazine Ser. 5, 50(302), 157-175.
• Siddiqi, N. (2006). Credit Risk Scorecards: Developing and Implementing Intelligent Credit Scoring. Wiley.

Regulatory references

• Basel (BCBS CRE 32.4): regulatory PD floors (0.05% for corporate, bank and retail; 0.03% or exempt for sovereign).
• EBA/GL/2017/16: guidelines on the specification, estimation, and validation of PD/LGD parameters in IRB models.
• IFRS 9: the mathematical framework for staging, ECL and asymmetric threshold optimization is documented in docs/methodology.md §8.6, but the executable implementation of ECL = PD × LGD × EAD, staging, and asymmetric threshold optimization is planned for Phase 7 and is not implemented in 1.0.0rc4.
• SR 11-7 / OCC 2011-12: model risk management (MRM) guidance.

License

Apache License 2.0 — see LICENSE.

Contact

Marco Rengel — marcrengel@gmail.com — github.com/Marco-Rengel

Translations

• Español (Spanish)