I would reduce the deforestation and help people get more practical education especially in poor and violent areas where kids are forced to take jobs because they don't get proper education, practical education in the sense making them learn about Cryptcurrency and Bitcoins, getting them hands-on internship etc, I think education for knowledge to earn money is way out of poverty which is one of the black-mark in our society, would love to get your opinions and thoughts on how you would impact the world when you are a billionaire.
If I'm billionaire because of holding bitcoin, then I will make a school or any learning facilities that help especially for poor people. Because with education, we can move foward into global competition. Also I'm going to teach about bitcoin ( from intro until how to spend it) because bitcoin is amazing currency that will help people on the future.