-s <tree>, --source=<tree>
Restore the working tree files with the content from the given tree. It is common to specify
the source tree by naming a commit, branch or tag associated with it.
If not specified, the contents are restored from HEAD if --staged is given, otherwise from the index.
As a special case, you may use "A...B" as a shortcut for the merge base of A and B if there
is exactly one merge base. You can leave out at most one of A and B, in which case it
defaults to HEAD.