Japan’s securities watchdog has conducted a probe at the headquarters of MUFG Bank, one of the country’s megabanks, over an employee’s alleged involvement in insider trading, sources familiar with the matter said Tuesday. The employee allegedly gave to a family member information about a client’s prospective tender offer before the bid became public. The relative netted several million yen from trading stock based on the information, according to the sources. “We have indeed been inspected, but we decline to comment further due to the ongoing investigation. We will fully cooperate with authori…