What would be the correct term for a single instance of a multiverse?

I am trying to write (some fiction) about how the (singular) universe got shattered into a multiverse (collective noun?)

I tripped up when I wanted to refer to one of the instances (or branches if you will) of the multiverse.

Multiverse (singular) seems ambiguous with the whole multiverse (all of the single instances). Like wise using universe is also ambiguous; a single instance or the single thing which got shattered.

To further complicated matters I want to refer to a sub set of instances (e.g., the instances where 'Alex' dies in a car crash)

So what would be a useful or clear way to refer to:

1. A singular Universe?
2. A collective multiverse?
3. A single instance, or branch, of the multiverse?
4. A sub set of the multiverse instances?

If your story hinges on The Many Worlds of Hugh Everett -- and it sounds as though it could -- then branch is undeniably correct. Branch could also be understood for other multiverse theories, but it may not be technically accurate -- on that, I don't know. With the Hugh Everett theory, the multiverse continues to branch with each and every quantum "decision".