text: to make sure that root remains black is color
code: root -> color = false ; root = insert ( root , 20 ) ; root -> color = false ; root = insert ( root , 30 ) ; root -> color = false ; root = insert ( root , 40 ) ; root -> color = false ; root = insert ( root , 50 ) ; root -> color = false ; root = insert ( root , 25 ) ; root -> color = false ;