to make sure that root remains black is color
root . color = false ; root = node . insert ( root , 20 ) ; root . color = false ; root = node . insert ( root , 30 ) ; root . color = false ; root = node . insert ( root , 40 ) ; root . color = false ; root = node . insert ( root , 50 ) ; root . color = false ; root = node . insert ( root , 25 ) ; root . color = false ;