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.
Input: root = [1,2,3,4,5,6,7], to_delete = [3,5] Output: [[1,2,null,4],,]
Input: root = [1,2,4,null,3], to_delete =  Output: [[1,2,4]]
to_delete.length <= 1000
to_deletecontains distinct values between