Hard copy put up in tree (5)
I believe the answer is:
birch
'tree' is the definition.
(I know that birch is a type of tree)
'hard copy put up' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'copy' becomes 'crib' (crib can mean to copy from another source).
'put up' says the letters should be written backwards.
'h'+'crib'='hcrib'
'hcrib' back-to-front is 'BIRCH'.
'in' acts as a link.
(Other definitions for birch that I've seen before include "to beat the rest?" , "Tree, beat" , "Tree - used in corporal punishment" , "Tree, maybe silver" , "Silver-white barked tree" .)