The most common and most likely answer to this crossword clue is the 4 letter word ACAI
I've seen this crossword clue in The Times
A
C
A
I
More clues leading to the result ACAI
- Tree has saccharin, shedding odd bits
- Berry used in aphrodisiac — ardour mounting
- Ace American’s one nicking intro from Chuck Berry
- Two articles, one being about first appearance of Chuck Berry
- Berry that’s apparently complex antioxidant import – for starters
- Tree in Maracaibo yielding saccharin now and then
- Fruit from WI a cargo brought over?
- Healthy food – an even distribution of fruit in saccharin
- Berry found in Maracaibo
- Berry that's apparently complex antioxidant import – for starters
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 = acai.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 ACAI mean?
ACAI noun- Any of several South American palms, of the genus Euterpe, having a dark purple drupe.
- The fruit of these trees, harvested for its juice.