Crossword Genius

Overly self-satisfied trees (4)

Ross

I believe the answer is:

gums

I'm a little stuck... Click here to teach me more about this clue!

'trees' is the definition.
(gum is a kind of tree)

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for gums that I've seen before include "Glues" , "Teeth are set in them" , "Trees" , "Smug around the mouth" .)

I've seen this clue in the Sydney Morning Herald.
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