public void nonSortedTree() {
        System.out.print(root.key+" ");
        recursiveNonSortedTree(root.left, root.right);
    }

    private void recursiveNonSortedTree(Node left, Node right) {
        if (left != null) {
            System.out.print(left.key+" ");
        }
        if (right != null) {
            System.out.print(right.key+" ");
        }

        if (left != null) {
            recursiveNonSortedTree(left.left, left.right);
        }
        if (right != null) {
            recursiveNonSortedTree(right.left, right.right);
        }
    }