This example shows an interactive tree diagram built with D3.js, where clicking a node collapses or expands its children with smooth animated transitions. The data is a hardcoded JSON structure representing a family hierarchy, with names like Roshan and Nimmat. The code uses `d3.layout.tree` to compute node positions and `d3.svg.diagonal` to draw curved links between parent and child nodes. Node and link elements are rendered as SVG circles, text, and paths, with transitions handled by D3's `transition` API.