Sort parent tasks only

I experienced a few times already issue about sorting tasks with dates.

Case: Parent tasks with due date. They contain subtasks that have no due date (since it can be done in any time).

While using "Sort by Due Date" it will always throw child tasks on end of list, instead keep them under parents. It may be expected behaviour for some users. However would be nice to make sorting affecting only parent tasks so child tasks stays under them.