Get commits added to the branch by api


I’m testing GitLab and also the way to get some information using the api. Most of my requirements can be achieved very easily but there is one thing where I’ve no idea how to do that. My goal ist to get the commits (ids) that were committed to a branch after the branch has been created. I would expect, that there must be an information about the starting point of the branch (e.g. id, timestamp,…) and I can take all commits after that point - but it seems that there is not such information and I can only get the last commit of the branch.

I think this is not a special requirement and it must be possible, because the graph (see picture below) is also able to show that, but mabe it’s the wrong approach and there is another way to do that. Any ideas?