Collection class involving other collections (a la TreeView/TreeNodes)

Hey everybody,
Looking for another push in the right direction here.
I'm trying to create a class that involves other collection, like the Treeview has Treenodes, which have treenodes, which have treenodes, etc...
I have a Treeview that holds Teams, then Processors assigned to those teams, and then Tasks assigned to those Processors. I need to fill an excel spreadsheet based on these assignments. I'd like to create instance of a class based on each parent node in the treeview (where level == 0), where I can say 'foreach (Alpha alpha in Processor), create headers in excel, and so on and so on...
I've got classes created, but I'm afraid I've only got it set up where I can create a Team.Processors, and a Processors.Alpha, but not a Team.Processors.Alphas...
Any ideas or detailed articles on this?
Thanks!
Scott