Trees

A tree is a kind of graph, composed of nodes and links, such that:

• A link is a directed pointer from one node to another.

• One node, called the root, has no incoming links.

• Each node, other than the root, has exactly one incoming link from its parent.

• Every node is reachable from the root.

A node can have any number of children. A node with no children is called a leaf ; a node with children is an interior node.

Trees often occur in computer systems and in nature.