This example visualizes COVID-19 statistics as an interactive tree graph, showing cumulative confirmed cases, deaths, and recoveries for several countries organized by continent. The hierarchy is computed using `d3.hierarchy` and laid out with `d3.tree`, a treemap layout algorithm that positions nodes based on their hierarchical relationships. Nodes are rendered as filled circles with descriptive text labels, while curved paths connect parent and child nodes. The data is embedded directly in the JavaScript source rather than loaded from an external file.