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
- 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.