tree with papery bark (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tree with papery bark</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 birch that I've seen before include "Type of tree" , "Flogging rod" , "Hardy tree" , "Tree with grey or white bark" , "to beat the rest?" .)