This example shows a tidy radial tree diagram of human blood group types. The visualization maps major blood groups (A, B, AB, O) to their positive and negative Rh factor variants, with each generation assigned a distinct fill color. Built with D3 v6, the code uses `d3.stratify()` to convert the parent-child data into a hierarchy and `d3.tree()` for layout. SVG circles, text labels, and path links are animated into place using D3's `.transition()` API.