This example displays a hierarchical tree of US regions and states, with a root "United States" node branching into Eastern and Western regions and their constituent states. The visualization uses D3.js v7's `d3.tree()` layout function with `d3.hierarchy()` to structure the data, and renders the tree as an SVG using `d3.linkHorizontal()` for curved link paths. Node circles and text labels are positioned through the tree layout's coordinate system, while the canvas size adapts to the viewport dimensions.