Definition of Tree(recursive):
A root node connecting to a number of trees
Root:
with no parents
Parent and child:
Every node except the root has exactly only 1 parent
A node can have zero or no children
Leaves:
no children
Siblings:
nodes with the same parent
Path:
From node n1 to nk a sequence of nodes
Length:
Number of edge on the path
Depth:
The length of the unique path from root to the node
Height:
Length of the longest path from the node to a leaf
All leaves are at height 0
Height of a tree
Height of the root
depth of the deepest leaf
from n1 to n2
n1 is an ancestor of n2
n2 is an descendant of n1
if n1 ≠ n2, proper ancestor and proper descent