Rogue has to leave floundering Theresa May, say (4)

I believe the answer is:

tree

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

'may say' is the definition.
'tree' can be an answer for 'may' (I've seen this before). I'm not sure about the 'say' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tree that I've seen before include "Large, woody perennial plant" , "Large shrub; family line" , "Elder, possibly" , "trod the boards" , "Beech, for example" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app