This interactive tree diagram visualizes the classification of matter, using an animated, collapsible layout to show the hierarchical relationships between categories like pure substances, mixtures, elements, and compounds. The visualization is built with D3.js v3 and uses the `d3.layout.tree` API to compute the graph structure. Node colors and link styling are applied dynamically through custom CSS and JavaScript functions, with tooltips that appear on hover. The data is loaded from a JSON file containing the hierarchical structure.