Frame that's attached to pan in storeroom, did you say? (4)

I believe the answer is:

tree

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'say?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for tree that I've seen before include "Box or bay maybe?" , "Oak, for example" , "box, possibly" , "cross" , "Branching diagram" .)

I've seen this clue in The Guardian.

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