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