That feeling when you're trying to work and your brain is more interested in trying to concoct a clear graphical representation of your thoughts on space/multiverse/timelines...

For now, I'll just say that I don't think the involvement of multiple shards has anything to do with causing the split timeline, and you could cause the same effect through time travel within a single shard. Each version of the timeline carries a copy of all the shards in it - like a higher-level version of the Sundering where each shard was a copy of the same original thing but is now free to evolve separately.