The most common and most likely answer to this crossword clue is the 4 plus 4 letter word DATE PALM
I've seen this crossword clue in Independent
D
A
T
E
P
A
L
M
More clues leading to the result DATE PALM
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 = date palm.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.