1. The recursive base condition is : if both the roots are null , return true.
2. If either one of them is null, return false.
3. If the data of the root node of the first tree is not equal to the data of the root node of second tree, return false.
4. Check if the left subtree of the first tree is the mirror image of the right subtree of the second tree - isMirror(root1.left, root2.right).
5. Check if the right subtree of the first tree is the mirror image of the left subtree of the second tree - isMirror(root1.right, root2.left).
