Utilize the input text as a context reference, choose the right relationship between Optum and UnitedHealth Group from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

He joined the government in 2014, after working as an executive vice president at UnitedHealth Group Inc.'s Optum unit, which helped fix the main Obamacare website, healthcare.gov.

Answer: parent_organization