It would be great to have the option to use a parent task as a container. This means that, I would like to create a parent task of 10d estimation and fill it with sub-tasks with no estimation. Somehow marking it as a container would enable me to log time in the sub-tasks and have the parent task remaining time reduced. Meaning that work logged on sub-tasks should also be taken into account on parent task.

(this comes from a dedicated customer)