Oatly Group AB has formally filed paperwork on Monday for an initial public offering in the US., nine months after private-equity giant Blackstone Group Inc. and a handful of A-list celebrities took a stake in the oat milk producer. The Malmö, Sweden-based company set foot in the US market in 2017 with its alternative dairy products that have grown in popularity among consumers looking for healthier options with less repercussions on the environment.Last July, The Wall Street Journal reported the company had sold a $200 million stake to a group led by Blackstone and included Oprah Winfrey, Natalie Portman, former Starbucks Corp. chief Howard Schultz and the entertainment company launched by Jay-Z. The sale of the roughly 10% stake valued Oatly at roughly $2 billion. In February, the oat-milk maker confidentially filed for an IPO in the US. The retail value of the plant-based dairy industry in the Americans is expected to hit $7 billion by 2025, according to Euromonitor.