Negotiate to wander around certain valuable collection (8,5)
I believe the answer is:
treasure trove
'collection' is the definition.
(I know that treasure trove is a type of collection)
'negotiate to wander around certain valuable' is the wordplay.
'negotiate' becomes 'treat' (I've seen this in another clue).
'to wander' becomes 'rove' (synonyms).
'around' is an insertion indicator.
'certain valuable' becomes 'sure' (I can't explain this - if you can you should give a lot more credence to this answer).
'treat'+'rove'='treatrove'
'treatrove' enclosing 'sure' is 'TREASURE-TROVE'.
Can you help me to learn more?
(Other definitions for treasure trove that I've seen before include "stash?" , "Hidden delights" , "lot of valuable things" , "valuable discovery" , "asset to the government" .)