He is not only the president of the Debate Club but also the captain of the Basketball team.
What type of sentence is this sentence?

The correct answer is- Compound Sentence.

Compound Sentence:
- যে বাক্যে একাধিক Principal Clause 'Coordinating Conjunction' দ্বারা যুক্ত থাকে তাকে Compound Sentence বলে।

এই বাক্যে দুটি independent Principal clauses আছে:
Clause 1: He is the president of the Debate Club.
Clause 2: He is the captain of the Basketball team.
এই দুটি independent clause কে Coordinating Conjunction: "not only ... but also" দিয়ে যুক্ত করা হয়েছে। তাই এটি একটি compound sentence.

Compound Sentence গঠনের শর্ত হচ্ছে-
- বাক্যে একের অধিক Principal Clause থাকবে।
- বাক্যে এক বা একাধিক Coordinating Conjunction থাকবে।
and, or, but, both, fewer than, neither, and, not only.... but also, no less than, neither... nor, either... or, otherwise, still, yet, else, nevertheless, on the contrary, only, so, therefore, consequently, for- ইত্যাদি Coordinating Conjunction দ্বারা Compound Sentence গঠিত হয়।

Source: A Passage to the English Language, S. M. Zakir Hussain.