Shoppers browse clothing inside an Untuckit store at the King of Prussia mall in King of Prussia, Pennsylvania, Oct. 20, 2018.

Men have worn untucked shirts for years. When a company came along to sell only shirts that are designed to be untucked – not surprisingly that market turned out to be pretty lucrative.

That company, known as Untuckit, has hired a prominent investment bank to raise money and help fuel its growth, according to people familiar with the situation. Untuckit is seeking a deal that will value it at more than $600 million and has Morgan Stanley out looking for the funds.

In doing so, it follows a similar path forged by other brands like sustainable sneaker brand AllBirds, which in October raised $50 million from T. Rowe Price, Fidelity and Tiger Global.

Untuckit has roughly $150 million in sales and is profitable, the people said. It raised $30 million from venture firm Kleiner Perkins last June, reportedly valuing it at more than $200 million.

The people asked not to be named because the information is confidential. Untuckit and Morgan Stanley declined to comment.

Untuckit is the brainchild of Executive Chairman Chris Riccobono and CEO Aaron Sanandres. Riccobono had been struggling to find a dress shirt that wasn't too big or too baggy. He worked to develop a professional solution with his fellow Columbia Business School classmate.

The two launched the brand online in 2011. Four years later, they opened its first brick-and-mortar store in New York's SoHo district. The co-founders were early believers in the idea that e-commerce companies can benefit from storefronts, which can help to alleviate marketing and delivery costs.

Untuckit now has 50 stores nationwide and has said it aims to open 100 stores over the next five years.

The brand has also expanded beyond men who want to go untucked. It now sells shirts, dresses, tees and jackets for women, as well as shirts and bottoms for boys.

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