Well,
First, you should capitalize the first word of each sentence.
I love ice cream it is the best treat in the world
Now, obviously we have to put punctuation somewhere in the middle of the sentence. We could put a period, a semicolon, or an exclamation mark after the word "cream." For the punctuation after the word "world," we could put a period or an exclamation mark.
I love ice cream. It is the best treat in the world.
I love ice cream; it is the best treat in the world.
I love ice cream! It is the best treat in the world.
I love ice cream. It is the best treat in the world!
I love ice cream; it is the best treat in the world!
I love ice cream! It is the best treat in the world!
Different punctuation will produce different effects. For example: the first sentence had the least excitement, while the last sentence had the most excitement.