This collapsible tree diagram displays hierarchical employee data, organized by department such as Operation, Technology, and HR & Admin. The visualization uses a D3 tree layout with SVG rendering and animated transitions to expand and collapse nodes on click. Built with d3.hierarchy and the d3.tree() API, the code reads hierarchical data from a JavaScript object and applies a diagonal path generator for curved links. Node circles and text labels update their positions smoothly over a 750-millisecond duration, with collapsed nodes remaining visible via a lighter blue fill.