Definitions for "Directory tree"
hierarchy of directories
The branching structure of directories on a disk, starting at the root directory. The root of the tree is usually considered as the of the structure, so the actual structure can be visualized as an upside-down tree with the root at the top and branches going down.
UNIX uses a hierarchical structure for organizing files and directories. This structure is often referred to as a directory tree . The tree has a single root node, the slash character ( /), and all other directories are contained below it.
Keywords:  recursion, example
an example of recursion