Show the union of two views rather than the intersection

Issue Summary

I would like to use Views Fusion so that I can quickly see what parent nodes don't have children associated with them, and what child nodes don't have parents associated with them. For example, if the nodes looked like this:

Parent 1 ___________
Parent 2 ___________
Parent 3 ----> Child 1
Parent 4 ----> Child 2
____________ Child 3
____________ Child 4

Currently, a fused view would only show:

Parent 3 ----> Child 1
Parent 4 ----> Child 2

I would like it to show all of the parents and children.

Thanks