For two trees to be mirror images , the following three conditions must be true 1 - Their root node 's key must be same  2 - left subtree of left tree and right  subtree of right tree have to be mirror images  3 - right subtree of left tree and left subtree  of right tree have to be mirror images
if ( node1 != null && node2 != null && node1 . key == node2 . key ) return ( isMirror ( node1 . left , node2 . right ) && isMirror ( node1 . right , node2 . left ) ) ;