A tree diagram visualizes a retrosynthetic analysis pathway for a chemical substance, with branching paths representing alternative synthesis routes and precursor compounds. Each node is labeled with its substance URI, and connecting links are drawn as horizontal paths. The visualization uses D3 version 5’s `d3.tree` layout, `d3.hierarchy`, and `d3.linkHorizontal` to compute positions and link paths, rendering to an SVG canvas. Data is loaded from a JSON file containing nested precursor and reaction alternatives.