A shaky-looking tree (5)
I believe the answer is:
aspen
This clue could be a double definition.
'a shaky' is the first definition.
(thesaurus)
'looking tree' is the second definition.
'aspen' can be an answer for 'tree' (aspen is a kind of tree). I'm not sure about the 'looking' bit.
Can you help me to learn more?
(Other definitions for aspen that I've seen before include "Trembling poplar tree" , "Very timid" , "Tremulous poplar" , "Type of poplar" , "winter resort" .)