Inserting an element into a highly unbalanced binary search tree containing N nodes will take time _______.

Inserting an element into a highly unbalanced binary search tree (BST) will take time proportional to the height of the tree. In the worst-case scenario, where the tree is entirely unbalanced (like a linked list), the height of the tree can be N, where N is the number of nodes.

1. Time Complexity: The time complexity of insertion in a binary search tree is O(h), where h is the height of the tree.

2. Unbalanced Tree Case: In a highly unbalanced binary search tree, the height can reach N (inserting elements in sequential order without balancing), leading to:

   $O(N)$

Thus, inserting an element into a highly unbalanced binary search tree containing N nodes will take time O(N) in the worst-case scenario.