How to re-use subworkflow in UML activity diagram

I'm trying to model a pipeline in UML as an activity diagram, and I'm not sure how to describe a process consisting of multiple steps, where the user can decide which parts to execute:

-case 1: only A
-case 2: A and B
-case 3: A, B and C (Note: B can not be skipped in order to process C)

But if I put it into an activity diagram, I have to draw each sub-workflow multiple times:

So I don't think I'm doing it right. Maybe someone could help me with it?

Solution

In the end what I was looking for was a nested activity as shown in https://softwareengineering.stackexchange.com/questions/331641/how-do-i-represent-nested-actions-in-a-uml-activity-diagram