Too has 3 different meanings across 1 category:
Adverb
to a degree exceeding normal or proper limits
"too big"
in addition
"he has a Mercedes, too"
Likewise.
The word "too" comes from Middle English and Old English, where it originally meant "also" or "in addition." This sense developed from the preposition's original meaning of "to" or "into," which implied being apart or separate.