WEX (WEX) was Smart Insider's stock pick of the week after the company's Chief Executive Melissa Smith bought more than $500,000 worth of the company's shares for $134.57 apiece on May 29, raising her stake by 2%.

This was Smith's first share purchase since October 2008 and her largest so far, Smart Insider said in a note Tuesday.

"It's encouraging to see a long-serving key executive officer making the largest purchase to date, and at the highest price on record," the note said.

The stock purchase by Smith, who is also the company's chair and president, is a reversal from a "long series of sales" and the second largest investment by any insider since 2005, according to the note.

Smart Insider ranked the stock +1, or strong positive signal, on June 3.