It’s tall, like some Christmas trees (4)
I believe the answer is:
mast
'it's tall' is the definition.
I can't judge whether this defines the answer.
'some christmas trees' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'MAST' is hidden in the letters of 'christmas trees'.
'like' acts as a link.
Can you help me to learn more?
(Other definitions for mast that I've seen before include "Upright transmitter; fruit of oak trees" , "Main vertical spar of vessel" , "Long vertical pole" , "Supporting pole, for radio aerial, perhaps" , "One carries the sails of a ship" .)