This example shows a tree diagram that visualizes hierarchical data loaded from an external JSON file. The diagram uses a horizontal layout where parent nodes appear on the left and child nodes extend to the right, with circular markers and text labels for each node. The visualization is rendered as an SVG, built with d3.js v5, using the `d3.tree()` layout algorithm, `d3.hierarchy()` for structuring parent-child relationships, and `d3.json()` for asynchronous data loading. The data itself is a simple family tree with a top-level node, two second-level nodes, and two leaf nodes.