This example shows a hierarchical tree visualization of programming languages and their subcategories, with nodes colored by generation depth. The visualization uses D3 v7 and renders SVG elements, including vertical links drawn with `d3.linkVertical()` and nodes positioned via `d3.tree()`. The flat parent-child data is converted into a hierarchy using `d3.stratify()`. The root node appears in red, middle-level nodes in blue, and leaf nodes in green, with each node labeled by its name.