Given tree
TreeNode root = new TreeNode ( 20 ) ; TreeNode left = new TreeNode ( 12 ) ; TreeNode right = new TreeNode ( 18 ) ; root . children . Add ( left ) ; root . children . Add ( right ) ; left . children . Add ( new TreeNode ( 11 ) ) ; left . children . Add ( new TreeNode ( 3 ) ) ; right . children . Add ( new TreeNode ( 15 ) ) ; right . children . Add ( new TreeNode ( 8 ) ) ;