This interactive tree chart depicts the hierarchical structure of COVID-19 data, including variants, symptoms, and their associated percentages and medications. The visualization uses a D3.js layout with expandable and collapsible nodes, allowing users to click on a node to reveal or hide its children. It employs SVG rendering with animated transitions (`duration` and `transition`) for smooth updates, and uses a `d3.layout.tree()` for node positioning and `d3.svg.diagonal()` for link paths, with styles for the circle, text, and path elements defined in the HTML.