BinaryTree

 public class TreeNode
    {
        public int val;
        public TreeNode left;
        public TreeNode right;

        public TreeNode(int x)
        {
            val = x;
        }
    }

      private void WriteTreeNode(TreeNode node)
        {
            StringBuilder stringBuilder=new StringBuilder();
            if (node == null)
            {
                Console.WriteLine("node is null");
                return;
            }

            stringBuilder.Append($"node is {node.val}");
            if (node.left == null)
            {
                stringBuilder.Append(", node.left is null");
            }
            else
            {
                stringBuilder.Append($", node.left is {node.left.val}");
            }
            if (node.right == null)
            {
                stringBuilder.Append(", node.right is null");
            }
            else
            {
                stringBuilder.Append($", node.right is {node.right.val}");
            }
            Console.WriteLine(stringBuilder.ToString());

            if (node.left != null)
            {
                WriteTreeNode(node.left);
            }
            if (node.right != null)
            {
                WriteTreeNode(node.right);
            }
        }