Just as Elon Musk is set to become the world's first trillionaire, Vanguard's S&P 500 ETF also is the first to hit $1 trillion-in-assets.

Investors and fund companies alike are incresingly betting on active exchange-traded funds.

Just as Elon Musk is set to become the world's first trillionaire, Vanguard's S&P 500 ETF also is the first to hit $1 trillion-in-assets.