it compares two given trees and return '0' two trees are same
else return '1' two trees are different.
execute 'fun' function-----if both tree roots are null then it returns '0'(means two are same)
-----------------------------------if one tree root is null and other is not it returns '1'(means two are different)
------------------------------else compare left subtree and right subtree(there is or condition between left and right subtree.if left subtree value is not equal to left subtree of another tree it returns '1'.and no need to compare right subtree because or operation is always returns '1')
so ans is B