A little Googling shows that Treston is an uncommon but widespread surname in English speaking countries. For example, we have:
Jim Treston, a realtor in Jacksonville, Florida:
http://bestjacksonvillerealestate.com/
Sherry S. Treston, a lawyer in Chicago:
http://www.sidley.com/lawyers/bio.asp?id=7335
Quinlan, Miller & Treston, a law firm in Brisbane, Australia:
http://www.qmtlaw.com.au/
Ben Treston, a director of commercials and music videos based in
London, England:
http://www.bentreston.com/director/Home.html
Michael Treston, youth co-ordinator of an Anglican diocese in New Zealand:
http://www.emergingchurch.info/stories/cafe/michaeltreston/index.htm
So Treston is undoubtedly a normal surname originally from somewhere in the British Isles. In spite of all these references, it must be fairly rare since it is not mentioned in either Hanks & Hodges'
A Dictionary of Surnames or Reaney &
Wilson's
A Dictionary of English Surnames. There is also no place called Treston mentioned in A.D. Mills'
A Dictionary of English Place-Names. So you would have to do genealogical research on the Treston surname to discover what its origin is. You can't assume that the first syllable is linked to "trees" without research, however. The place name in Mills' book that does begin with Tres-, Treswell, derives that from an Old English given name, Tir.