Git only tracks “upstream” information in individual repositories and this information is not static nor shared between separate clones of the same repository.
The command to set this relationship from the command line is:
git branch --set-upstream <branch> [<start-point>]
Looking at the output of git-diff might give you a clue:
git diff <mybranch>..master # commits in master that are not in mybranch
git diff <mybranch>..2.2 # commits in 2.2 that are not in mybranch
It is likely that the one with fewer commits listed is the branch point (but that is not guaranteed, obviously.
You can also use gitk, or git log to take a look around:
gitk --all
git log --graph --color --decorate --oneline --all