A vertical tree diagram visualizes a food hierarchy using rectangles for nodes, starting with "Food" and branching into Vegetables and Fruits, then further into specific items like Spinach and Apple. The D3.js v7 code uses `d3.hierarchy` to process the nested JSON data and `d3.tree` to compute the layout. SVG paths with curved bezier links connect the nodes, while styled rectangles and text labels render each element with colors defined in CSS.