The most common and most likely answer to this crossword clue is the 6 letter word ELDERS
I've seen this crossword clue in The Guardian
E
L
D
E
R
S
Buddy explains!
The straight part
We know that "trees" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trees = elders.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 ELDERS mean?
ELDERS noun- An older person or an older member, usually a leader, of some community.
- One who is older than another.
- One who lived at an earlier period; a predecessor.
- An officer of a church, sometimes having teaching responsibilities.
- A clergyman authorized to administer all the sacraments.
- One ordained to the lowest office in the Melchizedek priesthood.
- Male missionary.
- (often capitalized) Title for a male missionary; title for a general authority.
- A pagan or Heathen priest or priestess.
- To admonish or reprove for improper conduct by the elders of the meeting.
- A small tree, Sambucus nigra, having white flowers in a cluster, and edible purple berries
- Any of the other species of the genus Sambucus: small trees, shrubs or herbaceous perennials with red, purple, or white/yellow berries (some of which are poisonous).