The Hubert you refer to appears to be a grandson of the Hubert Treston born 1803 (probobly in Mayo)and married to Rose Fullam 17th July 1824 in DunLaoghaire (refered to elsewhere on this message board). His youngest son Michael Treston (born 1849 & married to Ester Lynch 1881) emigrated as you indicate but to South America and is claimed to have returned, but no evidence of his death cert in Dublin. They registerered the birth of one son Hubert Tressin in 1886, whose marriage to Mary Roe on 7th Feb 1907 is recorded as Tresson. Hubert (1886) registered the birth of 12 childern in the names Treston, Trestin, and Tresson
The family at Cottage(Mayo) to which you refer has spelt their name Treston from at least the late 1600s to the current day. The family had moved from Roscommon into Mayo. There are records going back to 1585,& 1582 of Trostan and Tristan names in Roscommon which appears to be the orins for the Cottage Treston.
Hope this helps?