Preserve business graduate found in tree (6)
I believe the answer is:
embalm
'preserve' is the definition.
(as in embalming a body)
'business graduate found in tree' is the wordplay.
'business graduate' becomes 'MBA' (Master of Business Administration degree).
'found in' means one lot of letters goes inside another.
'tree' becomes 'elm' (elm is a kind of tree).
'mba' going within 'elm' is 'EMBALM'.
(Other definitions for embalm that I've seen before include "Make into mummy" , "Preserve corpse from decay" , "Treat corpse with preservatives" , "Prepare for burial" , "Use chemicals to preserve a dead body from decay" .)