This example shows a hierarchical tree visualization of patient records, displaying each patient as a leaf node labeled with their last name. The layout is computed using `d3.stratify` to structure the flat patient data and `d3.tree` to calculate node positions. Links between nodes are drawn as cubic Bézier curves using SVG paths, with circles representing each node and text labels positioned relative to children. The visualization is embedded in a React-compatible HTML page, though the provided code uses plain JavaScript with D3 v5 and renders entirely to SVG.