The most common and most likely answer to this crossword clue is the 5 letter word ROWAN
I've seen this crossword clue in The Times
R
O
W
A
N
More clues leading to the result ROWAN
- Member of rose family Rosa, but it’s become pale and sickly
- Tree line primarily advancing north
- Wife stuck in chestnut tree
- Owl, dropping wings, lands in chestnut tree
- Horse must pass round wide tree
- Tree Reagan planted outside Washington
- Dispute over a new tree
- Argument over a name for a tree
- Argue about origin of native tree
- Egyptian god carrying round ankh with new tree
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 = rowan.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 ROWAN mean?
ROWAN noun- Sorbus aucuparia, the European rowan.
- Any of various small deciduous trees or shrubs of genus Sorbus, belonging to the rose family, with pinnate leaves, corymbs of white flowers, and usually with orange-red berries.
- A second crop of hay; aftermath.
- A stubble field left unploughed until late in the autumn, so that it can be cropped by cattle.