A hierarchical tree diagram visualizes global health data, organizing countries as parents, disease categories as their children, and individual diseases as leaves. The layout uses a vertical tree structure where nodes are color-coded by depth: orange for countries, blue for categories, and green for diseases. Custom data is rendered as an SVG using D3 v7, employing `d3.hierarchy` to structure the data and `d3.tree` with `d3.linkVertical` to compute and draw the paths. Node circles are styled with inline fills based on depth, with text labels positioned above each node.