Do iterative traversal of second tree and find first lead node in it as " temp2"
Node temp2 = s2 . Peek ( ) ; s2 . Pop ( ) ; while ( temp2 != null && isLeaf ( temp2 ) != true ) { s2 . Push ( temp2 . right ) ; s2 . Push ( temp2 . left ) ; temp2 = s2 . Peek ( ) ; s2 . Pop ( ) ; }