A Bubble Universe is a variation of the Core Universe. If the Core Universe is the tree's trunk, then a Bubble Universe is the tree's branches. As the Bubble Universes grow out away from the tree trunk, they become less and less alike to other Bubble Universes, but still hold similarities to the Core Universe.
Bubble Universes seldom hold the same locations and planets. They may have all started in a certain way that was more alike to each other, but as the independent universes have their own conditions and events happening within them, the outcomes have created vastly different landscapes. For example, Earth in the Core Universe is how Earth is to them, but Earth in a Bubble Universe could have been destroyed by an asteroid or never even existed due to conditions in the start of that universe.
However, as odd as it may seem, there has been no discovery of intelligent life other than the Humans of the Core Universe.