Complex sentence: The Treble Choir is the only junior choir in SPCC and the members are usually from Form 1-3, while the Concert Choir and the Senior Mixed Voice Choir mainly consist of Form 3-7 members.
Split into simpler sentences: The Treble Choir is the only junior choir in SPCC and the members are usually from Form 1-3. On the contrary, the Concert Choir and the Senior Mixed Voice Choir mainly consist of Form 3-7 members.