In Julius Caesar, what was the purpose of having the two soldiers come and sleep in Brutus’ tent?

Brutus tells Varro and Claudius that he wants them to sleep in his tent because he may have to wake them to take a message to Cassius. I think that Shakespeare also has them there so that Brutus was not alone when the ghost of Caesar comes to him. After the appearance of the ghost, Brutus wakes both Varro and Claudius but although Lucius spoke in his sleep, neither of them heard anything of the ghost. Thus the only other potential witnesses to the ghostly visitation saw and heard nothing, calling into question the veracity of the visitation. Did Caesar truly return, or was the ghost a figment of Brutus' guilty conscience?