Treston does appear to be a surname (although that may or may not have been the origin of your classmate's name - it could just be a variation of
Tristan influenced by
Trenton).
the 'ton' part is certainly 'town', but I can't see any evidence for or against 'tres' meaning 'trees'. Perhaps someone with a better knowledge of Old English can make a suggestion?
♦ Chrisell ♦
All we have to decide is what to do with the time that is given us. - J.R.R. Tolkien.