      "        in_order_traversal(node, self.results.add_result)\n",
      "        assert_equal(str(self.results), '[1, 2, 3, 5, 8]')\n",
      "        self.results.clear_results()\n",
      "\n",
      "        node = Node(1)\n",
      "        insert(node, 2)\n",
      "        insert(node, 3)\n",
      "        insert(node, 4)\n",
      "        insert(node, 5)\n",
      "        in_order_traversal(node, self.results.add_result)\n",
 
</s>
    "        node = insert(None, 1)\n",
      "        in_order_traversal(node, self.results.add_result)\n",
      "        assert_equal(str(self.results), '[1, 2, 3, 5, 8]')\n",
      "        self.results.clear_results()\n",
      "\n",
    "        node = insert(None, 1)\n",
      "        insert(node, 2)\n",
      "        insert(node, 3)\n",
      "        insert(node, 4)\n",
      "        insert(node, 5)\n",
      "        in_order_traversal(node, self.results.add_result)\n",
keep keep keep keep replace keep keep keep keep keep
 Polish bst challenge and solution

Add root is None input test case.  Update time and space complexity discussion.
graphs_trees/bst/bst_solution.ipynb