Add Decision Tree (Cây Quyết Định) interactive lesson

[LMK89]

Summary

Added a comprehensive interactive educational lesson on Decision Trees (Cây Quyết Định) in Vietnamese, featuring visual explanations, 4 state comparisons, live demo, and self-grading quiz.

Key Changes

• New lesson file: 2026-08-25-decision-tree-3d45ae7c.html — complete standalone HTML lesson covering:

  • Definition and core concepts of decision trees
  • Real-world bank loan approval use case with sample data
  • 4 tree states comparison: Root Only (underfit) → Shallow Tree → Balanced Tree (optimal) → Deep/Overfit Tree
  • Comprehensive comparison table showing accuracy trade-offs across states
  • Interactive demo allowing users to input customer data and trace tree traversal step-by-step
  • Good vs. bad data characteristics section
  • 3-question self-grading quiz with instant feedback

• Updated README.md: Added entry for the new Decision Tree lesson to the course index

Implementation Details

• Responsive design with CSS custom properties supporting light/dark theme toggle
• Interactive features:
  • Live tree traversal demo with animated step-by-step output
  • Random data generator for testing
  • Quiz with immediate feedback and score calculation
• Visual hierarchy: Uses numbered sections, colored pills, ASCII tree diagrams, and animated transitions
• Educational focus: Emphasizes the bias-variance tradeoff and overfitting concepts through concrete examples
• Accessibility: Vietnamese language, clear explanations, practical code snippets using scikit-learn

https://claude.ai/code/session_0198CbF99ZMqTggi1s5zg6WD