Delete Nodes And Return Forest

Given the `root` of a binary tree, each node in the tree has a distinct value. After deleting all nodes with a value in `to_delete`, we are left with a forest (a disjoint union of trees). Return the roots of the trees in the remaining forest. You may return the result in any order.   **Example 1:** **Input:** root = [1,2,3,4,5,6,7], to_delete = [3,5] **Output:** [[1,2,null,4],[6],[7]] ``` **Example 2:** **Input:** root = [1,2,4,null,3], to_delete = [3] **Output:** [[1,2,4]] ```   **Constraints:** - The number of nodes in the given tree is at most `1000`. - Each node has a distinct value between `1` and `1000`. - `to_delete.length <= 1000` - `to_delete` contains distinct values between `1` and `1000`.