-- https://www.merriam-webster.com/grammar/plural-of-bus
Went ahead and used Google Ngram viewer to show the popularity difference, with some context-words to ensure it's comparing cases where a plural noun is being used:
https://books.google.com/ngrams/graph?content=the+busses%2C+...
https://books.google.com/ngrams/graph?content=multiple+busse...
https://books.google.com/ngrams/graph?content=took+buses%2C+...