The most common and most likely answer to this crossword clue is the 5 plus 3 letter word MINCE PIE
I've seen this crossword clue in The Daily Telegraph
M
I
N
C
E
P
I
E
More clues leading to the result MINCE PIE
- A viewer of EastEnders Christmas special?
- The London Eye?
- Mushroom I found during dig that will be eaten at Christmas?
- London Eye can be a Christmas treat
- Mushroom I put in my fancy pastry
- Chop up bird cooked and eaten at Christmas
- Naughty niece, imp wanting something for Christmas?
- An eye for a Cockney‘s Christmas treat?
- Cut up good English Xmas treat
- This writer’s going round church with holy Christmas fare
Buddy explains!

The straight part
We know that "Xmas treat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case xmas treat = mince pie.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.