Where can I find info on how to shrink build size

Unity Engine
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1

Main Menu and 1 level =56 meg build.
Main menu and 3 levels= 85 meg build.

How can i find what is causing this meg increase? This is basically saying 10 megs per level, how can I find what this stuff is and remove or compress? I have compressed everything i can, but not sure what is left to do.

2

Check Unity Editor log. It prints the sizes of assets included into build.

http://unity3d.com/support/documentation/Manual/Reducing%20File%20size.html