This example displays a three-layer biological taxonomy tree for the animal kingdom, organizing species under their respective classes beneath the root kingdom Animalia. The visualization uses D3.js v7 with the `d3.hierarchy` and `d3.tree` layout APIs to position nodes, while `d3.linkHorizontal` draws the connecting edges between hierarchical levels. Node colors and radii encode depth, with the root, class, and species layers distinguished by distinct hues. SVG rendering presents the tree with labels positioned to the left for parent nodes and to the right for leaf nodes.