This must be different for everyone, as many people see things differently to others. Therefore, everyone has their own personal universe as they percieve it, and they are all interlinked in some form of 'multiverse'.
However, if it is true that every decision creates new universes, for those it affects at least, then that must mean that there is an infinite number of multiverses. These then, must all co-exist within what I shall call the 'omniverse'. This is formed from every multiverse, all existing on exactly the same geographic X/Y/Z axes, but no affecting one another directly.
It is also possible that a choice may cause the merging of two multiverses. In order to rationalise this some method of distinguishing multiverses must be formed. For simplicity's sake I will compare the situation to that of phase differences of waves.
A simple way to imagine it, is with one multiverse, with a phase difference of 0. Every time a choice is made in that multiverse, a new multiverse is formed with a phase difference that is minutely larger than the previous (an increase of: one multiplied by ten to the power of negative infinity). Some choices have the capacity to decrease the phase difference, and so join multiverses together. This is very simplified but gives some impression of the process.