Check if a given tree graph is linear or not

Given a tree check if it is linear or not.

 1
 / \
 2 3
 Linear as we can
 form a line 2 1 3

 1
 / \
 2 3
 / \
 4 5
Not linear

Examples: 

Input : 3
1 2
1 3
Output :
YES
Explanation:
The Tree formed is 2-1-3 which is a linear one.

Input :
4
1 2
2 3
4 2
Output :
NO

Approach: The given tree would be linear only if n-2 of its nodes have indegree == 2 or number of nodes, n==1.  

Implementation:

YES