AngularJS: using input checkboxes and getting checked values from unrelated lists

I'm building a nested tree and using AngularJS input type checkboxes in all the leaves. Most of the examples I've seen use ng-repeat over a single list, bind the model to the list item, and then get the selected values.

But the items in my tree are all in different lists so I'm not sure how to bind them to the same model. What other ways are there or what solution is there to getting all the checked items without them being in the same model?