How do you play a toy accordion?

This is probably a stupid question, but how do you play the toy
accordion? It has 7 buttons, but 14 notes. The thing i'm confused
about is how to play both notes on one button. For example, the first
button is supposed to be for both notes C and D. How exactly do i get
it to play C and what do I do differently to get it to play D? Here is
what it looks like:
http://img.alibaba.com/photo/374732041/Toy_accordion.jpg

Thanks in advance! :)