This word is from the Spanish manzana (meaning: apple).
Note that the word mansanas with an ‘s’ at the end is both singular and plural. Most Spanish-derived Tagalog words are like that. Another example of a word having an ‘s’ at the end yet used as both singular and plural: prutas
Kumain ka ng mansanas.
Eat an apple.
Bumili ako ng dalawang mansanas.
I bought two apples.
Apples are not native to the Philippines. It wasn’t until import liberalization in the 1980’s did it become easier to buy apples outside U.S. military bases.