San Francisco, Dec 28 (Reuters) - Tesla Inc (TSLA.O) Chief Executive Elon Musk on Tuesday completed stock sales related to his options set to expire next year, according to securities filings. The billionaire on Tuesday exercised an option to buy 1.6 million shares of Tesla and sold 934,090 shares for $1.02 billion to pay for taxes associated with the option exercise, the filings showed.