Consider the 'front page' of the Tasks App like http://easysocial.org/groups/12-test-group/44-tasks
I don't think it's as clear as it could be that Tasks are grouped within Milestones.
Could I suggest to solve this:
1) Each Milestone Listed actually starts with "Milestone: Name of Milestone
2) In the sidebar Statistics Widget, Milestones are listed first... that helps show they are 'bigger' than the tasks.