Jazzman in central London with a big tree (12)
I believe the answer is:
wellingtonia
'big tree' is the definition.
(I've seen this before)
'jazzman in central london with a' is the wordplay.
I cannot really understand how this works, but
'in' is within the answer.
'with' could be 'w' (abbreviation) and 'w' is present in the answer.
'a' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wellingtonia that I've seen before include "giant redwood" , "one grows tall" , "Tree - the big one" , "Sequoia" .)