I understand. Even though you have several rows of "All Milestones" in your BO, at the moment, "Querying" doesn't support Grouping functions and all.
So, if you wanna have the data filled in the Milestone column with all the Milestones "table", you will have to maintain all those Milestone instances in your BO and update then after when some modification happens!
OR
If you don't have sets of data for Milestone, you can always follow what Vinod said..
