This example shows a hierarchical tree visualization of movie data, grouped by distributor and genre, with the worldwide gross revenue aggregated for each group. The root hierarchy is built using `d3.rollup` and `d3.hierarchy`, then laid out with the `d3.tree` layout. Nodes are drawn as circles, connected by lines, with labels above and leaf counts below. The code uses D3 v7 APIs including `d3.sum`, `d3.select`, and `.join` to render the SVG elements.