This example visualizes the distribution of electric vehicle (EV) stock values for 2011 across four countries—China, India, the United Kingdom, and the USA. The hierarchical tree diagram branches into vehicle types (buses and cars) and further into powertrain categories (BEV and PHEV), with each leaf node’s value represented by its label. The chart uses a bespoke D3.js API (`d3.tree()`) to compute the layout, while custom SVG paths with quadratic Bézier curves draw the connecting links. Node and link colors are explicitly set via inline hex codes in the data structure, rendered as an SVG. The visualization is a fork of an existing tree-plotting example, demonstrating a custom layout approach.