Preserve tree invaded by many blessed ants initially (6)
I believe the answer is:
embalm
'preserve' is the definition.
(embalming is a kind of preserving)
'tree invaded by many blessed ants initially' is the wordplay.
'tree' becomes 'elm' (elm tree is a kind of tree**).
'invaded by' indicates putting letters inside.
'initially' says to take the initial letters.
The first letters of 'many blessed ants' is 'mba'.
'elm' going around 'mba' is 'EMBALM'.
(Other definitions for embalm that I've seen before include "Preserve body, mummify" , "Treat corpse so as to retard decay" , "Use chemicals to preserve a dead body from decay" , "Treat corpse with preservatives" , "Prepare corpse for preservation (6)" .)