This ghost is a representation of brutus’s feelings. This shows how confused he is and whats going through his mind at the moment. In addition brutus’s wife, portia just commited suicide in a very peculiar way she put hot coals on her mouth. Brutus is not metally stabled right now because everything has gone on to him and hebis starting to regret his actions against brutus this is why he is seeing caesar’s ghost ; his concience id torturing him.