"I've came..." as a result, what do you think of, Alexander?

Perfect всегда подразумевает «уже». Здесь упор не на то, что «вот я уже здесь», а на цель прихода: угостить тортом.

Ok, may be you're right.
So, past simple as a fact, right)?
But what about...
It seems to me, "to treat you TO a cake"...
?

В случае сомнения на счёт перфекта вставьте already и посмотрите, что получится: I’ve ALREADY come to treat you with a cake. Получилось несколько нелепо. Или уже был договор, что сосед принесёт торт, но тогда почему угостить? Обещал угостить?
Но тут простая фраза: пришёл, чтобы угостить.
Does it make sense?😊

I just checked with Ngram on treat you to, treat you with. The examples show this: treat you to an ice-cream and treat you with respect. So I corrected my translation.
https://books.google.com/ngrams/graph?content=treat+you+to%2Ctreat+you+with&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Ctreat%20you%20to%3B%2Cc0%3B.t1%3B%2Ctreat%20you%20with%3B%2Cc0

Sorry for the confusion😔

It's ok, Alex,
thank you for your help!☺

Welcome!

Uly, так значит все-таки "I've came"?
What about "I came..."
in this context?
Can I say "I came..." there?

... and thank you for your explanation about "I come bearing"👍

"I came" is a simple fact, "I've come" is an announcement. The perfect is used when you want to elevate something from a simple fact to a significant announcement: (Fact) I passed my exams. (Announcement) I've passed my exams. (finally!, thank God!). In this case, the speaker is announcing the reason for being at her neighbor's house - he isn't just coming over, he also brought cake(!).

👍🏼

Gala, it's "I've COME" (not CAME)

Also, TREAT usually means to pay for someone's food in a restaurant, etc. It can also mean to give someone something delicious to eat or drink, but we're using it less and less with that meaning.

One more thing - since one person usually doesn't eat a whole cake, it would be more correct to say "I came to treat you to cake" (not TO A CAKE).

Well, Uly, how about my translation with ‘to treat you to a cake’? I’ve never dealt with ‘to treat to’, just took it from dictionaries. And then, why do you use ‘cake’ without a/the?

Oh, exactly!😜
Of course, "I've come..." - I'd just mixed up the forms of the verb)
Thank you so much for interesting & useful explanation!

Thanks a Load, Uly!

Uly, if you don't mind, I'd like to ask about "I come bearing smth"...
If I didn't drink last night😀... and I just want to give a cake (a piece of cake) to my friend
(I mean - there is no guilty, I don't feel guilty towards my friend),
then...
is it correct to say - "I come bearing"?...

Absolutely. It just lets people know that you have something for them.

Okay, clear)
Thank you again!👍