You buy 2000 shares with your Roth IRA for $1 per share. They appreciate in value to $1,000 per share. You sell the shares, now there is $2,000,000 cash value

You buy 2000 shares with your Roth IRA for $1 per share. They appreciate in value to $1,000 per share. You sell the shares, now there is $2,000,000 cash value in your Roth IRA, which you can use to make other investments. Repeat ad infinitum without those transactions incurring any sort of tax burden, as long as you don't withdraw any of that money until you're 60.