To use the word tret is a mistake in academic English. Only in certain dialects does the word tret exist. In Hull, and some other Northern areas of England, this is the usual spoken past tense and past participle (the -ed forms) of the verb 'to treat'. A Hull speaker may say, fondly, "Me Mam tret me real nice", [more formally, "My Mother treated me extremely well"] or "He's been tret unfairly by the boss all along."
This article may help you to understand local dialect. Do not use tret in academic English writing. Stick to treated as the past forms, both past tense and -ed participle.