def _insert(self, data, current_node):
        if data <= current_node.data:
            if current_node.left is not None:
                self._insert(data, current_node.left)
            else:
                current_node.left = Node(data)
        else:
            if current_node.right is not None:
                self._insert(data, current_node.right)
            else:
                current_node.right = Node(data)