The most common and most likely answer to this crossword clue is the 7 letter word BOXWOOD
I've seen this crossword clue in Financial Times
B
O
X
W
O
O
D
More clues leading to the result BOXWOOD
Buddy explains!

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 = boxwood.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 BOXWOOD mean?
BOXWOOD noun- The box tree, Buxus sempervirens.
- The hard, close-grained wood of this tree, used in delicate woodwork and in making inlays.
- Any tree of genus Buxus.