Trembling poplar (5)
I believe the answer is:
aspen
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">trembling poplar</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for aspen that I've seen before include "Colorado ski resort - tree" , "winter resort" , "city in Colorado" , "that's wooden" , "quill-like?" .)