Secret store in a street tree (5)
I believe the answer is:
stash
'secret store' is the definition.
(I've seen this in another clue)
'street tree' is the wordplay.
'street' becomes 'st' (abbreviation).
'tree' becomes 'ash tree' (ash is a kind of tree).
'st'+'ash'='STASH'
'in a' acts as a link.
(Other definitions for stash that I've seen before include "Stow away" , "Squirrel away" , "drug store" , "Hide in a secret place" , "collection" .)