Plant tree after trimming decorations (8)

I believe the answer is:

refinery

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

'plant' is the definition.
(I know that refinery is a type of plant)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for refinery that I've seen before include "Chemical plant" , "Industrial processing plant (for, eg, oil)" , "Purification plant" , "Industrial plant for purifying a crude substance" , "Plant for purifying, oil say" .)

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

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