Задачи на деревья

- https://leetcode.com/problems/sum-of-left-leaves/
- https://leetcode.com/problems/find-mode-in-binary-search-tree/
- https://leetcode.com/problems/insert-into-a-binary-search-tree/
- https://leetcode.com/problems/find-elements-in-a-contaminated-binary-tree/
- https://leetcode.com/problems/deepest-leaves-sum/