-"git-diff-tree [--stdin] [-m] [-s] [-v] [--pretty] [-t] "
-"[<common diff options>] <tree-ish> <tree-ish>"
+"git-diff-tree [--stdin] [-m] [-s] [-v] [--pretty] [-t] [-r] [--root] "
+"[<common diff options>] <tree-ish> [<tree-ish>] [<path>...]\n"
+" -r diff recursively\n"
+" --root include the initial commit as diff against /dev/null\n"