``revisions``.

        :param message: message of the commit

        :param author: full username, i.e. "Joe Doe <joe.doe@example.com>"

        :param parents: single parent or sequence of parents from which commit

          would be derived

        :param date: ``datetime.datetime`` instance. Defaults to

          ``datetime.datetime.now()``.

        :param branch: branch name, as string. If none given, default backend's

          branch would be used.

        :raises ``CommitError``: if any error occurs while committing

        """

        self.check_integrity(parents)

        from .repository import GitRepository

        if branch is None:

            branch = GitRepository.DEFAULT_BRANCH_NAME

        repo = self.repository._repo

        object_store = repo.object_store

        ENCODING = b"UTF-8"  # TODO: should probably be kept in sync with safe_unicode/safe_bytes and vcs/conf/settings.py DEFAULT_ENCODINGS

        # Create tree and populates it with blobs

        commit_tree = self.parents[0] and repo[self.parents[0]._commit.tree] or \

            objects.Tree()

        for node in self.added + self.changed:

            # Compute subdirs if needed

            dirpath, nodename = posixpath.split(node.path)

            dirnames = safe_bytes(dirpath).split(b'/') if dirpath else []

            parent = commit_tree

            ancestors = [('', parent)]

            # Tries to dig for the deepest existing tree

            while dirnames:

                curdir = dirnames.pop(0)

                try:

                    dir_id = parent[curdir][1]

                except KeyError:

                    # put curdir back into dirnames and stops

                    dirnames.insert(0, curdir)

                    break

                else:

                    # If found, updates parent

                    parent = self.repository._repo[dir_id]

                    ancestors.append((curdir, parent))

            # Now parent is deepest existing tree and we need to create subtrees

            # for dirnames (in reverse order) [this only applies for nodes from added]

            new_trees = []

            blob = objects.Blob.from_string(node.content)

            node_path = safe_bytes(node.name)

            if dirnames:

                # If there are trees which should be created we need to build

                # them now (in reverse order)

                reversed_dirnames = list(reversed(dirnames))

                curtree = objects.Tree()

                curtree[node_path] = node.mode, blob.id

                new_trees.append(curtree)

                for dirname in reversed_dirnames[:-1]:

                    newtree = objects.Tree()

                    #newtree.add(stat.S_IFDIR, dirname, curtree.id)

                    newtree[dirname] = stat.S_IFDIR, curtree.id

                    new_trees.append(newtree)

                    curtree = newtree

                parent[reversed_dirnames[-1]] = stat.S_IFDIR, curtree.id

            else:

                parent.add(name=node_path, mode=node.mode, hexsha=blob.id)

            new_trees.append(parent)

            # Update ancestors

            for parent, tree, path in reversed([(a[1], b[1], b[0]) for a, b in

                zip(ancestors, ancestors[1:])]

            ):

                parent[path] = stat.S_IFDIR, tree.id

                object_store.add_object(tree)

            object_store.add_object(blob)

            for tree in new_trees:

                object_store.add_object(tree)

        for node in self.removed:

            paths = safe_bytes(node.path).split(b'/')

            tree = commit_tree

            trees = [tree]

            # Traverse deep into the forest...

            for path in paths:

                try:

                    obj = self.repository._repo[tree[path][1]]

                    if isinstance(obj, objects.Tree):

                        trees.append(obj)

                        tree = obj

                except KeyError:

                    break

            # Cut down the blob and all rotten trees on the way back...

                del tree[path]

                if tree:

                    # This tree still has elements - don't remove it or any

                    # of it's parents

                    break

        object_store.add_object(commit_tree)

        # Create commit

        commit = objects.Commit()

        commit.tree = commit_tree.id

        commit.parents = [p._commit.id for p in self.parents if p]

        commit.author = commit.committer = safe_bytes(author)

        commit.encoding = ENCODING

        commit.message = safe_bytes(message)

        # Compute date

        if date is None:

            date = time.time()

        elif isinstance(date, datetime.datetime):

            date = time.mktime(date.timetuple())

        author_time = kwargs.pop('author_time', date)

        commit.commit_time = int(date)

        commit.author_time = int(author_time)

        tz = time.timezone

        author_tz = kwargs.pop('author_timezone', tz)

        commit.commit_timezone = tz

        commit.author_timezone = author_tz

        object_store.add_object(commit)

        # Update vcs repository object & recreate dulwich repo

        ref = b'refs/heads/%s' % safe_bytes(branch)

        repo.refs[ref] = commit.id

        self.repository.revisions.append(ascii_str(commit.id))

        # invalidate parsed refs after commit

        self.repository._parsed_refs = self.repository._get_parsed_refs()

        tip = self.repository.get_changeset()

        self.reset()

        return tip

    def _get_missing_trees(self, path, root_tree):

        """

        Creates missing ``Tree`` objects for the given path.

        :param path: path given as a string. It may be a path to a file node

          (i.e. ``foo/bar/baz.txt``) or directory path - in that case it must

          end with slash (i.e. ``foo/bar/``).

        :param root_tree: ``dulwich.objects.Tree`` object from which we start

          traversing (should be commit's root tree)

        """

        dirpath = posixpath.split(path)[0]

        dirs = dirpath.split('/')

        if not dirs or dirs == ['']:

            return []

        def get_tree_for_dir(tree, dirname):

            for name, mode, id in tree.items():

                if name == dirname:

                    obj = self.repository._repo[id]

                    if isinstance(obj, objects.Tree):

                        return obj

                    else:

                        raise RepositoryError("Cannot create directory %s "

                            "at tree %s as path is occupied and is not a "

                            "Tree" % (dirname, tree))

            return None

        trees = []

        parent = root_tree

        for dirname in dirs:

            tree = get_tree_for_dir(parent, dirname)

            if tree is None:

                tree = objects.Tree()

                parent.add(stat.S_IFDIR, dirname, tree.id)

                parent = tree

            # Always append tree

            trees.append(tree)

        return trees