Upright part of a Christmas tree (4)
I believe the answer is:
mast
'upright part' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'of a christmas tree' is the wordplay.
'of' says the answer is hidden in the clue.
'MAST' is hidden within 'christmas tree'.
Can you help me to learn more?
(Other definitions for mast that I've seen before include "Long upright pole that supports sails" , "Pole on ship" , "Television transmitter" , "Pole supporting ship's sails" , "it rises on board a ship" .)