This example shows a hierarchical tree visualization of COVID-19 data, with a global root branching into continents, countries, and leaf nodes for cumulative confirmed cases, deaths, and recoveries. It uses the D3.js library, specifically the `d3.hierarchy` constructor and `d3.tree` layout, to compute node positions and render an SVG with styled circles and links. The data is embedded directly in the JavaScript, with each country node carrying a numeric value and color attributes that are not visualized further in the displayed output.