Maybe it's not new stuff. It's the same stuff. It would have to be, after all. The most efficient shape for it would be like a fizzy drink...in universe 1 I have sugar in my coffee, in universe 2, I don't. As in this model that changes exactly nothing (perhaps the next day the decision is the opposite, so I don't even have to change the day I buy sugar on or worry about possible diabetes over a life time.) universe 2 folds neatly back into universe 1 like a little bubble in order to conserve the multiverses energy.
Bigger events may create bigger bubbles, with bubbles within, divergent timelines that look straight or Web like....but assuming the universe has a begining and an end, the whole lot would fold out at point 1 and back in at part 2. And who knows, maybe back to the begining again like it's own big multiverse shaped bubble...if observed from outside. Much like the horizon is not a straight line.
I started writing a series of short stories about that, but the first one didn't sell or get much interest, so the project is in stasis until I find time to finish it.
Of course, that model explains things like quantum entanglement, spooky particles and where exactly all that dark matter is, but only from an imaginative point of view. I don't claim to be a physicist. And like Treks model, it works well enough for the story being told, and can't really be proven outright wrong. (it leads to a nice pub logic for atheism or religious belief belief ever having its respective nutters to stop being idiots too....if you conclusively prove God does not exist, another world exists where God is proven to exist by the same means. Since God is omnipotent etc, he then exists in all worlds, and in favt always would have done....disproving God would have the opposite effect. The reverse would also likely be true, as a universe with conclusive proof of God would create one where that conclusion was opposite, therefore God doesn't exist, because it's part of the nature of God the exist everywhere...if that doesn't happen, then it isn't God. So you can never ever prove or disprove the existence of God..
The multiverse won't like it... Now granted that all depends on your definition for God and proof etc, but as I said....it's amusing pub logic. I came up with it in a student bar. It's a bit of fun, not a statement, in case Dawkins Storm Troopers or Militant Religious Storm Troopers get all upset...my beliefs are my own, and may or may not be anything to do with this pub logic.)