I know that multiple git-trees can point to the same blob. This happens, when we only change the filename and do a commit again. But can there be git commits, that point to the same tree? If yes, when does it occur?
Sure...... a commom one, without thinking too hard: when you revert revisions, if you end up with the same tree (or several along the way of reverting many revisions)... well, there you have it.