only one reason for insiders to buy. That is the classic saying. I am usually not worried about insiders sell.
As for buy for the future sell, just think about it, if you want to do the same thing, will you do it, what is the success rate?
I think there are two reasons why a ceo would buy shares, mostly, he thinks risk/reward is very favorable. Another extreme situation is when the company is facing survival difficulties, founders have to come up with cash to increase market confidence on the company, but I do not think ATPG has any surviving problems. ATPG will have one well coming to production in a month. ATPG just sold 150 million dollar worth of preferred shares.