The most common and most likely answer to this crossword clue is the 8 letter word TAMARISK
I've seen this crossword clue in Financial Times
T
A
M
A
R
I
S
K
More clues leading to the result TAMARISK
Buddy explains!
The straight part
We know that "this tree" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this tree = tamarisk.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 TAMARISK mean?
TAMARISK noun- Any of several shrubs, of the genus Tamarix, native to arid regions in Eurasia and Africa, often invasive in other arid regions.