Humorous exchange - exchange for pear tree! (8)
I believe the answer is:
repartee
'humorous exchange' is the definition.
'repartee' can be an answer for 'exchange' (I have seen 'Witty exchange ' mean 'repartee' so perhaps 'exchange' could also mean 'repartee'). I'm unsure of the 'humorous' bit.
'exchange for pear tree' is the wordplay.
'pear tree' can be anagrammed to 'REPARTEE'.
But, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for repartee that I've seen before include "Lively exchange" , "Comic dialogue" , "Ready and witty retort" , "Ready wit" , "Witty comments" .)