Why is my IPA size 55 MB while my APK is only 25 MB?

When I build my game for iOS, the binary is more than twice the size of the same game built for Android.
The game is the same. Only iAds is added to the iOS build.

Why is there such a difference? Is that normal?

It could be that Android APK is ‘Packed’ like .zip or .rar and stuff like that, or uses better packing than iOS, there shouldn’t be any need to worry.