Abstract: Node-link data defining a graph also include tree defining data. The node-link data with the tree defining data further define a tree within the graph. The tree defining data indicate a set of elements in the graph that are represented in the tree. Each of a subset of elements in the set is represented more than once in the tree. For at least one element in the subset, the tree defining data indicate which representations of the element have descendants in the tree and which representations have none. The tree defining data can, for example, be expansion flags for links in the graph that are in the set of elements, with each links expansion flag indicating whether the link's to-node is expanded or contracted in the tree. In response to each of a series of expand and contract signals from a user, an iteration can modify the tree defining data and use it to present a representation of the graph with the indicated node expanded or contracted as requested.