/trattare/ is not reflexive, even if you use it in the form /si tratta/, it is the construct of the IMPERSONAL form, like /si dice/. Let's start from /si dice/ that is simpler. - si dice che la terra e` una sfera. Who says that? People say that! It is the impersonal form, with a precise meaning: - si dice che XYZ = la gente dice che XYZ (where XYZ is the secondary sentence). In this case the meaning of /si dice/ is explained by the use of the implicit subject /la gente/. What about /si tratta/ ? This is mote difficult, as it still is the IMPERSONAL form, but it does not have another standard way of rewriting it! /si tratta della cosa piu` importante/ Has the meaning: /the thing we are speaking of/ is for me the most relevant thing. So, in /si tratta/ the subject (which is NOT explicit) is the implied context. Example: A: guarda questo documento, per favore B: vedo, si tratta di una vendita di appartamneto, perche` ti interessa? Here /si tratta di XYZ/ means /il documento che sto guardando riguarda XYZ/, where XYZ is /una vendita di appartamento/ ------ A) cosa hai dentro quello zaino pesante? B) si tratta del materiale per una esplorazione in grotta. Here the implicit subject is: /il contenuto dello zaino/, and so the meaning is: Il contenuto dello zaino e` il materiale per una esplorazione in grotta. This is the meaning of /trattare/ like /it is/, /it relates to/ and so on. The other meaing of /trattare/ (to treat) follows a much easier grammar pattern: Io tratto bene il mio cane. Lui non si tratta molto bene. (true reflexive form) Gli esseri umani a volte si trattano molto male. (reciprocating reflexive form)

As a rule I never search over the internet (there are exceptions, when I have some doubts). My answers might be wrong or much better answers might be found online, but I presume that the asker is NOT a lazy person that does not want to search the internet, but he just enjoys a (even if virtual) conversation with a true human being, possibly with some DIRECT notions of the matter, so thanks to Mr. Juha and the many Askers who are interested in a conversation, even if within limits of time and space. in a kind of conversations.

Look here: http://www.wordreference.com/iten/trattare