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`.