This example displays a hierarchical tree visualization of hospital emergency room data, organized by department referral and showing individual patient details. Using D3.js v7, it fetches CSV data from a GitHub repository, transforms the flat records into a nested structure, and renders the result as an SVG tree layout. The visualization employs `d3.csv`, `d3.hierarchy`, and `d3.tree` to position nodes, with `d3.linkHorizontal` generating curved links between parent and child elements. Each patient node branches into leaf nodes for attributes like gender, age, date, and wait time.