Git symbolic-ref, Redmine & Repository setting
By default Redmine is used to track the master branch of a repository. Using git symbolic-ref, you can set-up the HEAD to point by default to another branch. The command use to achieve this is:
git symbolic-ref HEAD refs/heads/mybranch
From now on Redmine will default track the "mybranch" branch when visiting the Repository tab. Read more documentation on the Git manual.