If someone tries it with only .10 BTC I can double it.
If no one tries then you will never no if it's a scam.
It obviously IS either a pyramid, or a scam. If you could double money like that, then why don't you double your own ? (because it works only 50% of the time, right)
It's just because no one else TRIES THIS. It's not a pyramid because I only need one person. And I wouldn't scam people out of .10 BTC