This document defines common tree terminology used in computer science. It explains that a tree is a set of vertices with one root vertex and other vertices arranged in subtrees. It defines key terms like nodes, degrees, edges, levels, ancestors and descendants. Examples are provided to illustrate a tree structure and how terms like root, parent, child, sibling apply to different nodes in the tree. Common tree traversal and processing concepts are also covered briefly.

1. TREE Terminologies
By,
Dr. Gopika S
Department of CS
Kristu Jayanti College , Bengaluru

2. Trees
Tree is a finite set of vertices that has a vertex called
as root and remaining vertices are collection of
subtrees.
Dr. Gopika S , KJC , Bengaluru 2

3. Dr. Gopika S , KJC , Bengaluru 3

4. Dr. Gopika S , KJC , Bengaluru 4

5. 5
Node Degree
• Node degree is the number of children it has
Dr. Gopika S , KJC , Bengaluru

6. 6
Tree Degree
• Tree degree is the maximum of node degrees
tree degree = 3
Dr. Gopika S , KJC , Bengaluru

7. subtree
Tree Terminology
• Root: node without parent (A)
• Siblings: nodes share the same parent
• Internal node: node with at least one
child (A, B, C, F)
• External node (leaf ): node without
children (E, I, J, K, G, H, D)
• Ancestors of a node: parent,
grandparent, grand-grandparent, etc.
• Descendant of a node: child,
grandchild, grand-grandchild, etc.
• Depth of a node: number of ancestors
• Height of a tree: maximum depth of
any node (3)
• Degree of a node: the number of its
children
• Degree of a tree: the maximum
number of its node.
A
B D
C
G H
E F
I J K
Subtree: tree consisting of a
node and its descendants
Dr. Gopika S , KJC , Bengaluru 7

8. • Path: traversal from node to node along the edges that results in
a sequence
• Root: node at the top of the tree
• Parent: any node, except root has exactly one edge running
upward to another node. The node above it is called parent.
• Child: any node may have one or more lines running downward
to other nodes. Nodes below are children.
• Leaf: a node that has no children
• Sub tree: any node can be considered to be the root of a subtree,
which consists of its children and its children's children and so
on.
• Visiting: a node is visited when program control arrives at the
node, usually for processing.
• Traversing: to traverse a tree means to visit all the nodes in some
specified order.
• Levels: the level of a particular node refers to how many
generations the node is from the root. Root is assumed to be
level 0.
Dr. Gopika S , KJC , Bengaluru 8

9. • Some Terminology
– node: the item of information plus the branches to each
node.
– degree: the number of subtrees of a node
– degree of a tree: the maximum of the degree of the
nodes in the tree.
– terminal nodes (or leaf): nodes that have degree zero
– nonterminal nodes: nodes that don’t belong to terminal
nodes.
– children: the roots of the subtrees of a node X are the
children of X
– parent: X is the parent of its children.
Dr. Gopika S , KJC , Bengaluru 9

10. –siblings: children of the same parent are said to
be siblings.
–Ancestors of a node: all the nodes along the
path from the root to that node.
–The level of a node: defined by letting the root
be at level one. If a node is at level l, then it
children are at level l+1.
–Height (or depth): the maximum level of any
node in the tree
Dr. Gopika S , KJC , Bengaluru 10

11. • Example
A is the root node
B is the parent of D and E
C is the sibling of B
D and E are the children of B
D, E, F, G, I are external nodes, or leaves
A, B, C, H are internal nodes
The level of E is 3
The height (depth) of the tree is 4
The degree of node B is 2
The degree of the tree is 3
The ancestors of node I is A, C, H
The descendants of node C is F, G, H, I
A
B C
H
I
D E F G
Level
1
2
3
4
Property: (# edges) = (#nodes) - 1
Dr. Gopika S , KJC , Bengaluru 11

12. Thank you
Dr. Gopika S , KJC , Bengaluru 12