Hey, you certainly can, but would need separate tables for your tasks, and subtasks.
Your subtask table would need a lookup field in it to link subtasks to it's parent task. If you wanted the view like that above, you'd have to use the list view, like Scott said above, and use the 'Levels' menu to show Tasks, with linked sub-tasks below. They can both have unique fields / headers but it's the only way I can think of doing it.