Think and believe can be inserted elements, but strictly speaking, they can't be called parenthesis, but parenthesis is like, to be honest, I like her very much. To tell the truth, this is parenthesis, just an infinitive phrase, and Tom likes that girl very much, I think. I think this is parenthesis, subject and predicate. Tense, generally speaking, the tense of a clause cannot exceed the tense of the main clause. Specifically, the main clause is the future tense, so the clause should be the present tense or later tense, but everything has its own particularity and cannot be generalized. Pay attention to special circumstances when studying.