The most common and most likely answer to this crossword clue is the 6 letter word CORNEL
C
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The straight part
We know that "tree" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tree = cornel.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CORNEL mean?
CORNEL noun- Any tree or shrub of the dogwood subgenera, Cornus subg. Arctocrania (syn. Cornus subg. Chamaepericlymenum) or Cornus subg. Cornus, especially Cornus mas, the European cornel.
- The cherry-like fruit of such plants, certain of which are edible.