An updatable tree diagram displays hierarchical data with labeled nodes and curved links, rendered as an SVG. The code uses the d3.js library’s `d3.tree` layout and `d3.hierarchy` to compute node positions, then draws node circles and text via `d3.select` and SVG group elements. Link paths are generated with a custom `crossDiagonal` function that creates curved, cubic Bézier curves, and the tree updates by appending new nodes and links to the scene.