This example presents a hierarchical tree diagram of global health data, organizing countries into disease categories and specific diseases beneath a “Global Health” root. The visualization uses an SVG-drawn tree layout, with colored nodes indicating depth: orange for countries, blue for disease categories, and green for individual diseases. The code builds the hierarchy with `d3.hierarchy()`, positions nodes using `d3.tree()`, and connects them with `d3.linkVertical()` paths. Labels appear above each circle, and the layout is calculated dynamically based on the 800×800 SVG dimensions.