public static void levelOrder(Node root) {
        Queue<Node> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty()) {
            Node current = queue.poll();
            System.out.print(current.data+" ");
            if(current.left != null) queue.add(current.left);
            if(current.right != null) queue.add(current.right);
        }

    }