Unexpectedly mark up trees in shop (11)
I believe the answer is:
supermarket
'shop' is the definition.
(thesaurus)
'unexpectedly mark up trees' is the wordplay.
'unexpectedly' is an anagram indicator.
'mark'+'up'+'trees'='markuptrees'
'markuptrees' anagrammed gives 'SUPERMARKET'.
'in' is the link.
(Other definitions for supermarket that I've seen before include "Large shop" , "Grocery store" , "Large store selling food and household supplies" , "Large retail outlet" .)