This visualization presents a hierarchical tree of world countries organized by continent and subregion, rendered as an interactive SVG. The root node labeled "Blood Group" branches into major regions such as Western Asia and South-Eastern Asia, with country names as leaf nodes. Using D3 v5, the code applies a `d3.tree()` layout and `d3.linkHorizontal()` to draw curved links between parent and child nodes. Panning and zooming are enabled through D3's `d3.zoom()` behavior on the SVG element, with text labels sized dynamically based on depth.