A hierarchical tree visualization displays the countries of the world organized by region, using a horizontal node-link layout rendered as SVG. The code builds the tree with D3's `d3.hierarchy` and `d3.tree` functions, then draws curved links via `d3.linkHorizontal` and positions text labels from the nested data structure in `data.json`. Interactive pan and zoom are enabled through D3's zoom behavior, while the `Playfair Display` font and green link strokes style the final presentation.