This example shows an interactive collapsible tree hierarchy, allowing users to click on nodes to expand or collapse their children, and to navigate the tree by re-rooting it at a clicked node. The visualization uses D3.js v6 to compute a tidy tree layout with `d3.hierarchy` and renders it as an SVG, with animated transitions for all changes. A custom node-info div displays the name and ID of the last clicked node. The code also manages a stack to remember previous roots, enabling backward navigation through the hierarchy.