Tree - lots of trees - in LA suburb (9)
I believe the answer is:
hollywood
'la suburb' is the definition.
(Hollywood is a neighbourhood of Los Angeles)
'tree lots of trees' is the wordplay.
'tree' becomes 'holly' (holly is a kind of tree).
'lots of trees' becomes 'wood' (I've seen this before).
'holly'+'wood'='HOLLYWOOD'
'in' acts as a link.
(Other definitions for hollywood that I've seen before include "California suburb" , "There's a place for tinsel" , "Where Frankie goes" , "Cinematically brash and romantic" , "in LA?" .)