This example shows an animated, collapsible tree diagram built with D3.js v3, displaying hierarchical data loaded from a JSON file. The tree layout positions nodes by depth, and clicking a node toggles its children in or out with smooth transitions. The visualization uses `d3.layout.tree`, `d3.svg.diagonal` for curved links, and SVG elements for circles and text labels. Node and link styling uses pink circles and gray paths, with all interactions handled by a click function that updates the layout.