Is it possible to sing in 2 different notes at one time as a singer?

I'm not sure exactly, it's either notes or tones in vocals, but ive heard plenty on how Chester Bennington is able to sing in two different pitches within one note, like at the same time, my friend told it's impossible and i don't know, so if you could tell me if it's possible or what songs he does it in it would be highly appreciated. =]