A collapsible tree visualization maps the hierarchical structure of Wikipedia categories, comparing the number of subcategories between Russian and English versions. Node color encodes the difference in subcategory counts, with a legend explaining the scale. The visualization uses D3 v5’s `tree` layout and `linkVertical` path generator to position SVG circles and links, with `d3.scaleLinear` mapping group values to a purple-to-white color range. Zoom and pan are enabled via `d3.zoom`, and the data is loaded asynchronously from a JSON file using `d3.json`.