The most common and most likely answer to this crossword clue is the 10 letter word DISCOURSED
I've seen this crossword clue in The Daily Telegraph
D
I
S
C
O
U
R
S
E
D
Buddy explains!
The straight part
We know that "treated formally" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case treated formally = discoursed.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 DISCOURSED mean?
DISCOURSED verb- To engage in discussion or conversation; to converse.
- To write or speak formally and at length.
- To debate.
- To exercise reason; to employ the mind in judging and inferring; to reason.
- To produce or emit (musical sounds).