The most common and most likely answer to this crossword clue is the 9 letter word SASSAFRAS
S
A
S
S
A
F
R
A
S
More clues leading to the result SASSAFRAS
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 = sassafras.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 SASSAFRAS mean?
SASSAFRAS noun- A tree of species Sassafras albidum of the eastern United States and Asia having mitten-shaped leaves and red, aromatic heartwood.
- A tree of any species in the genus Sassafras.
- The bark of the root of this plant, used for medicinal and (mostly historically) culinary purposes and formerly a main ingredient in root beer.