Oh, that's nesting (I always known it as subtasking). Astrid doesnt do to that level of nesting "in-app" and it only imports. I think it could be done on Producteev then you sync it to Astrid. However, I havent tried the pro version yet, as I myself is still testing several task apps to see which would fit my needs best.
Another free app (currently in my phone but not being used yet) is WAToDo! Lite, but it only supports one level of subtasking (a little better than Astrid) apart from grouping, tagging and listing. Paid version has unlimited levels for subtasks.
- Easily Create, Update and Delete Tasks
- Assign Priorities to Tasks
- Assign Task as Next Action
- Attach Notes to Tasks
- Repeating Tasks
- Agile To-Do Management using Getting Things Done Methodology
- Collect actionable tasks via Inbox, Someday/Maybe list
- Create, Review & Manage Tasks in Task Lists
- Make Multi-Action Tasks into Sub-Projects
- 1 Level of Sub-Projects (Get Full Version for unlimited)
- Review Tasks via Task Lists, Projects or Tags
- Group Task by Due Date,Priority
- Tag Tasks and Projects and Filter them by ALL/ANY Tags
- Various Settings to change views
You should try Mobile Project Manager if you're willing to pay and need more than one subtask level, costs about $6 (using local conversion rate as my market shows local currency):
-import from mpp, xml, or Excel
-Unlimited nesting of tasks
-Multiple predecessors
-HTML/Excel Gantt reporting
-set up tasks as child or predecessors, even multiple predecessors!
-export/import Excel - use to share with your team!
-HTML summary report
-link files, contacts,notes, etc
-Import/Export MS Project format - as XML or Excel
-List dependent tasks
-Link to contacts assigned when they match first and last name - your resources can then be called or emailed for a status report in just a couple of clicks!
-Search tasks within your project
-Producteev.com task sync for online task management and reminders*
-Supports app 2 sd installs to sdcard (Froyo - 2.2 OS or higher)
- Gr8 4 PMP
- Resources management
- unique view of current tasks across projects
- resource view features a list of all tasks assigned to a selected resource
https://market.android.com/details?id=com.hawkmoon.mpm&feature=search_result