def expand(self):
old_expanded = [[]]<EOL>for sub in self._tree:<EOL><INDENT>sub_expanded = sub.expand()<EOL>new_expanded = []<EOL>while len(old_expanded) > <NUM_LIT:0>:<EOL><INDENT>sentence = old_expanded.pop()<EOL>for new in sub_expanded:<EOL><INDENT>new_expanded.append(sentence + new)<EOL><DEDENT><DEDENT>old_expanded = new_expanded<EOL><DEDENT>return old_expanded<EOL>
Creates a combination of all sub-sentences.

Returns:
    List<List<str>>: A list with all subsentence expansions combined in
                        every possible way