その文は英語文に合わないと思う。
「一杯機嫌」　酒に酔って、気持ちよさそうにしていること。

Lit up like a Christmas tree:
1. Covered in or decorated with many bright lights.
2. Very brightly or radiantly illuminated.

I'm not sure, but the following websites say:
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https://eow.alc.co.jp/search?q=...christmas+tree
lit up like a Christmas tree
＝ drunk
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https://tokuhain.arukikata.co.j...tmas_tree.html
"lit up like a Christmas Tree"
「クリスマスツリーのライトのように明るく」という意味から派生して
「クリスマスツリーのライトのように赤く酔っ払って」の意味。
なんでも「とにかくいい感じで酔っ払っている」というときにぜひ。
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If they're true, that link doesn't sound too bad to me(, even though it's not a literal translation). Let's ask English native speakers.

@AlanF_US, @sundown, @CK, @DJ_Saidez
Can we use this expression[#31441] for someone who (at a party and so on) is getting drunk faster than the others around, and looking pleasant?

@small_snow

I can't remember hearing the expression used that way, but there are so many idioms to describe someone who is drunk that I'm sure it might be. I usually hear this expression used in a more literal way. Imagine someone on their bicycle when it's getting dark who has several lights attached to the frame and the wheels and is wearing bright, reflective clothing. You could say of them that they're lit up like a Christmas tree.

You wrote "looking pleasant". Perhaps you meant something like "looking merry". "Merry" is often used to describe someone who is in high spirits and on their way to getting drunk. :)

@sundown
Thanks for your detailed explanation!

And...

>You wrote "looking pleasant". Perhaps you meant something like "looking merry". "Merry" is often used to describe someone who is in high spirits and on their way to getting drunk. :)

Thank you!! 😇 φ(..) note note