Ability to add select all button for "Deliverables" tag

It is not convenience to select all used tasks under "Deliverables" tag. User have to manually select or use "shit" to select. So, is it able to add such function. and there is no multiple unselect function.

If user select the parent task, the children tasks were not be selected at this time. user have to select them manually. It is able to add the function as when select parent task, then default to select all children tasks belong to this parent task?