YMCA terribly vexed about tree (8)
I believe the answer is:
sycamore
'tree' is the definition.
(I know that Sycamore is a type of tree)
'ymca terribly vexed about' is the wordplay.
'terribly' indicates an anagram.
'vexed' becomes 'sore' (I've seen this in another clue).
'about' is an insertion indicator.
'ymca' is an anagram of 'ycam'.
'ycam' put into 'sore' is 'SYCAMORE'.
(Other definitions for sycamore that I've seen before include "Tree, form of maple" , "Tree for the odd Rose Macy" , "The tree is strangely so creamy" , "Eurasian maple-tree" , "Deciduous tree" .)