def _put(self, root: TreeNode, key):
if root.key == key:
root.key = key
elif key < root.key:
if root.hasLeftChild():
self._put(root.leftChild, key)
else:
root.leftChild = TreeNode(key, root)
self._size += 1
else:
if root.hasRightChild():
self._put(root.rightChild, key)
else:
root.rightChild = TreeNode(key, root)
self._size += 1
