Here it is my problem: I use SourceTree to manager my work,while my colleague use Tortoisegit.
but we are in the same branch -- master,and I notice that the graph has many branchs:(the repository has only a master),why?there is not other branch..
and they sometimes commit a merge:
It confuses me,i throught merge in git is happened between two branchs,and i did review the documentation of merge:https://git-scm.com/book/en/v2/Git-Branching-Basic-Branching-and-Merging.