A single patient record from the cardio_train.csv dataset forms a small hierarchical tree, with the cardio status as the root and eleven other attributes—age, gender, height, weight, blood pressures, cholesterol, glucose, and lifestyle flags—as leaf nodes. The visualization uses D3.js v6 with a tree layout, rendering nodes as colored circles and connecting them with horizontal links. The code reads the semicolon-delimited file via `d3.dsv`, converts coded values to readable text, and maps the data into a hierarchy using `d3.hierarchy` and `d3.tree`.