(Reuters) - The State of Michigan Retirement System, which oversees some $143.9 million in pension fund assets for state employees, has invested $6.6 million in the ARK 21Shares Bitcoin ETF, it disclosed in a regulatory filing on Friday.

This marks the second confirmed investment by a pension fund in the spot bitcoin exchange-traded funds (ETFs) launched in January, a sign the assets are slowly beginning to attract traditional institutional investors in a boost for crypto assets.