Preserve business qualification in tree (6)
I believe the answer is:
embalm
'preserve' is the definition.
(as in embalming a body)
'business qualification in tree' is the wordplay.
'business qualification' becomes 'mba' (I am not sure about this - if you are sure you should believe this answer much more).
'in' means one lot of letters goes inside another.
'tree' becomes 'elm' (elm is a kind of tree).
'mba' inserted inside 'elm' is 'EMBALM'.
Can you help me to learn more?
(Other definitions for embalm that I've seen before include "Use chemicals to preserve a dead body from decay" , "Preserve from decay in death with chemicals" , "Make into mummy" , "Prepare for burial" , "Preserve body, mummify" .)