How to merge product structures from 2 different environments?

How to merge product structures from 2 different environments?
We have a complex product CP that has been modified in 2 different environments, with different changes. We want to keep the changes of both environments. How to merge these 2 changes?
What is the best approach?

E.g.  In environment A, the CP has got a new product N1. In environment B, the CP has got a new product N2

ENV A:

CP
- Child P
     - Grand Child P
     - N1

ENV B:

CP
- Child P
    - Grand Child P
- N2

After merge it should look like:

CP
- Child P
     - Grand Child P