The most common and most likely answer to this crossword clue is the 7 letter word ARBUTUS
I've seen this crossword clue in The Daily Telegraph
A
R
B
U
T
U
S
More clues leading to the result ARBUTUS
- Cutting from spectacular but useful shrub
- Unpopular, but usually accommodating growth
- Pointless war, but useful in part for Bush
- Bush was popular but useless to some extent
- Bush, a murderer, right at the top
- A conspirator twisted at first, seeking plant
- A Roman assassin moving right up in a tree
- A historic murderer runs up tree
- One Roman assassin’s head turned by something creepy in the garden
- … a group of plants from a royal bishop near Utah, America
Buddy explains!

The straight part
We know that "a tree" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a tree = arbutus.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 ARBUTUS mean?
ARBUTUS noun- A flowering plant in the genus Arbutus: the strawberry tree.
- Epigaea repens, the mayflower, the trailing arbutus.
- Arbute; the wood of the strawberry tree.