This example renders a hierarchical tree of world countries organized by continent and subregion. The visualization displays the geographic grouping structure with curved link paths connecting parent nodes to their children, starting from the root "World" node. It uses D3 v5 APIs including `d3.tree()` for layout, `d3.hierarchy()` for data structuring, and `linkHorizontal()` to generate the SVG paths. The data comes from a static JSON file loaded via `d3.json()`, with the SVG canvas sized to fill the viewport.