This interactive tree diagram, titled "EV Data Based on Countries," visualizes a nested hierarchy of electric vehicle statistics. It displays a root node for overall EV data, which branches out to country-level nodes (Australia, Austria, Belgium), then to vehicle type categories (Cars, Buses, Trucks), and finally to powertrain types (BEV, PHEV, EV). The code constructs the visualization using D3.js version 7, and the page structure is defined in `index.html` with styling from `style.css`. The JavaScript builds the tree layout and renders it as SVG elements, with links styled as gray lines and circular nodes colored according to their level in the hierarchy.