This example shows a hierarchical tree of programming languages organized top-down, with root, category, subcategory, and leaf nodes distinguished by color. The visualization uses D3.js v7’s `d3.hierarchy` and `d3.tree` layouts to compute positions, then renders SVG paths via `d3.linkVertical` and circles with text labels. Node colors vary by depth, and hover interactions thicken circle strokes. The data is hardcoded in JavaScript with categories like Procedural, Object-Oriented, and Functional, each branching into specific languages.