This example shows a collapsible tree diagram of Indian states and districts, with each node representing a location and lines connecting parent-child relationships. The visualization uses D3.js version 3.5.17 with the `d3.layout.tree` and `d3.svg.diagonal` APIs to compute the layout and draw curved links. Nodes are rendered as SVG circles with text labels, and clicking toggles the expansion or collapse of branches. The tree animates with staggered transitions, adjusting node positions and link paths over 750 milliseconds. The data structure is a nested JavaScript object containing hierarchical geographic names.