This interactive tree diagram displays hierarchical data with collapsible nodes. The visualization uses the D3.js library (version 3.5.17) with a static JSON dataset containing a root node and its descendants. The code employs `d3.layout.tree` for layout computation and `d3.svg.diagonal` for link rendering. Users can click nodes to expand or collapse subtrees, triggering smooth animated transitions via D3's `.transition()` method. The SVG rendering includes styled circles and text labels, with nodes colored steelblue or lightsteelblue depending on collapsed state.