Basics of Tree Data Structure PART - 1 

  • Tree is a non-linear data structure which organizes data in a hierarchical structure and this is a recursive definition.
  • A tree is a connected graph without any circuits/cycles.

Tree Terminology-

The important terms related to tree data structure are-

1. Root-

  • The first node from where the tree originates is called as a root node.
  • In any tree, there must be only one root node.
  • We can never have multiple root nodes in a tree data structure.

Here, node A is the only root node.

 2. Edge-

  • The connecting link between any two nodes is called as an edge.
  • In a tree with n number of nodes, there are exactly (n-1) number of edges.

3. Parent-

  • The node which has a branch from it to any other node is called as a parent node.
  • In other words, the node which has one or more children is called as a parent node.
  • In a tree, a parent node can have any number of child nodes.


  • Node A is the parent of nodes B and C
  • Node B is the parent of nodes D, E and F
  • Node C is the parent of nodes G and H
  • Node E is the parent of nodes I and J
  • Node G is the parent of node K

4. Child-

  • The node which is a descendant of some node is called as a child node.
  • All the nodes except root node are child nodes.


  • Nodes B and C are the children of node A
  • Nodes D, E and F are the children of node B
  • Nodes G and H are the children of node C
  • Nodes I and J are the children of node E
  • Node K is the child of node G

5. Siblings-

  • Nodes which belong to the same parent are called as siblings.
  • In other words, nodes with the same parent are sibling nodes.

  • Nodes B and C are siblings
  • Nodes D, E and F are siblings
  • Nodes G and H are siblings
  • Nodes I and J are siblings

6. Degree-


  • Degree of a node is the total number of children of that node.
  • Degree of a tree is the highest degree of a node among all the nodes in the tree.




  • Degree of node A = 2
  • Degree of node B = 3
  • Degree of node C = 2
  • Degree of node D = 0
  • Degree of node E = 2
  • Degree of node F = 0
  • Degree of node G = 1
  • Degree of node H = 0
  • Degree of node I = 0
  • Degree of node J = 0
  • Degree of node K = 0
Remaining Tree Terminologies are discussed in my next article (Basics of Tree Data Structure PART - 2)
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