The only place I can find a Thomas Attree born Northiam is one born ca.1837 on the 1861 Census (married to Jane) where the surname is Tree and someone has added a comment to say surname should be Attree! - and then in 1901 and 1911 when Thomas and Jane living with son Rupert Attree.
However, the name Tree is correct - this Thomas was the son of a Charles and Eliza.
Thomas Tree married Jane Brown Dec.1856 Fareham and the 2 children with them on 1861 census were both born as 'Tree'. Indeed, the son Rupert's birth in 1871 is as Tree.
It is only after the 1871 census that this 'Tree' family become 'Attree'.
So, in 1841 Thomas is with his family in Northiam as 'Tree' (transcribed on Ancestry as Free).
Annette