Hi Ina, then could you tell me what's the difference between the two words? thanks in advanced.

Thanks, Ina :)

sorry, should be "threats"

I believe that what you meant to say was 'threats' not 'treats'. There is a big difference between those two.

Let's assume you are OK on the meaning of treats :) "Insider" is a noun, meaning one who belongs to some group or circle that excludes others. "Inside" in an adjective, meaning, more or less, contained within something.