This example displays a hierarchical tree of Earth's continents and countries, with each node represented by a circle and label. The tree layout is computed using `d3.tree()` and `d3.hierarchy()`, which assign parent-child relationships and spatial coordinates. Nodes and links are rendered as SVG elements: circles for nodes and horizontal curved paths for links, styled via CSS classes. The data is a static JavaScript object listing continents and selected countries, and the visualization uses D3 v6 within an HTML page.