A tree diagram visualizes the hierarchical relationship among dataset nodes, labeled "Truc" at the root and branching into child nodes such as "Truc1.1" and "Truc2.2." Built with D3.js (v3.5.17), the implementation uses the `d3.layout.tree` layout and `d3.svg.diagonal` for curved link paths. Nodes appear as white circles with steelblue strokes, connected by gray lines, and text labels are positioned to the left or right depending on whether they have children. The visualization renders with an animated transition, where nodes and links smoothly move to their assigned coordinates based on depth.