This example displays a small hierarchical tree of flight classes using D3.js. The visualization separates the data into two main branches, Basic and Premium, each with two child nodes, and lays them out horizontally using the `d3.tree` and `d3.hierarchy` APIs. It renders the structure as an SVG, drawing curved links with `d3.linkHorizontal()` and adding circular nodes and text labels for each element. The tree is generated from a static, embedded JavaScript data object, with all coordinates assigned by the layout algorithm before being drawn on an 800 by 600 canvas.