Utilize the input text as a context reference, choose the right relationship between Walgreens and Walgreens Boots Alliance 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.

Walgreen is part of Walgreens Boots Alliance Inc, and this year sold a majority stake in Trinity's parent Walgreens Infusion Services to private equity firm Madison Dearborn Partners.

Answer: parent_organization