Stack links to one link

Suppose I have 2 group of nodes, each group contains 10 nodes and there are 10 links between the group nodes, each node from one group is connected to one node in the other group.
When the 2 groups are collapsed, I see 10 parallel lines (links) between the groups.
How can I stack them into one “thick” line (link) ?
Tany Bahary

What if only one group is collapsed? What if there are multiple groups? What if there are nested groups?

Do you have some sketches or screenshots of what you want?

Also, what fromSpot and toSpot values are you using?