Samhain was a Celtic festival that originated in Ireland,most probably in Co Meath . The month of November is still called Samhain in the Irish Language. Lughnasa is the Irish for August and Bealtaine is Irish for May . It was an Irish festival exclusively.
Although Ireland played a major role in the development of the Gaelic festivals, those festivals are panCeltic in essence. Traces of the four festivals can be found in Scotland, Gaul and other places in Europe. This is well documented by academic research. Frederic Armao published a book called "Uisneach or the Center of Ireland" [Routledge, 2022] and a whole chapter is dedicated to this topic.
When I was growing up we'd dress up and knock on our neighbours doors. We'd ask for "Any apples or nuts" which would be what we'd be given. Never heard the expression "Trick or Treat" and sweets were rarely given out.