The most common and most likely answer to this crossword clue is the 8 letter word SOURWOOD
I've seen this crossword clue in The Guardian
S
O
U
R
W
O
O
D
Buddy explains!
The straight part
We know that "tree/tree" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tree/tree = sourwood.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 SOURWOOD mean?
SOURWOOD noun- A North American deciduous shrubby tree, of the genus Oxydendrum, having deep fissures in its bark, and sour-tasting leaves.
- An Australian tree, of the genus Hibiscus; the sorrel tree.