[commands] Only remove top level commands on cog load failure

discord/ext/commands/cog.py

@@ -408,6 +408,7 @@ class Cog(metaclass=CogMeta):
                 except Exception as e:
                     # undo our additions
                     for to_undo in self.__cog_commands__[:index]:
+                        if to_undo.parent is None:
                             bot.remove_command(to_undo.name)
                     raise e