Glossary » TreeMap
a diagram for representing hierarchical structures (trees). A TreeMap displays the hierarchy as a series of embedded boxes, where each box contains its children, usually by alternating at each level between laying them out vertically and laying them out horizontally.
The relative size of each box can be made proportional to some property where the parent’s property is the sum of the children. For instance, in a hierarchical file system, file size can be represented by the size of the leaf nodes, and each folder or directory is the size that is the sum of the size of the files within it.