Apple source (4)
'apple source' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tree that I've seen before include "Beech, for example" , "Genealogist's work" , "Oak, say" , "Large, woody perennial plant" , "elder, maybe" .)
(Other definitions for tori that I've seen before include "Large mouldings on columns" , "doughnuts" , "rings" .)