How to list multiple related jobs on CV

Say I have a position of project manager at my company A.

Now at the same time, I also have a sales related position on a company B, which is related to company A, say it is child company of A.

On my CV I have these positions listed chronologically and separately (both having date 2015-current).

e.g.

Project Manager at A, 2015-current
- item1
- item2

Sales Manager at B, 2015-current
- item1
- item2

When putting on Resume is it better to indicate somehow that B is related to A?

Otherwise someone might be surprised how person can have two positions on two different companies, whereas if I indicate, it will give them a hint that these companies are related, and hence less confusion.

Yes, you should showcase the relation between the jobs, to avoid confusion just as you mentioned.

Something like

Project Manager at A, 2015-current
- item1
- item2

Sales Manager at B (Wholly owned subsidiary of A), 2015-current
- item1
- item2

That said, I think you meant to write "2015", not "20015". You MUST NOT make these types of mistakes in the actual resume / CV.