Enable adding parallel activities in process variation

I would like to be able to add tasks in parallel in a process version. I can't do this and I can't change in the standard process either once I created variations.
The point here is to make sense of the process with tasks that start and are carried out at the same time. It is therefore not possible to use notes or a mini process to express this.
I find that such a restriction really blocks the use of process variations.
Thanks