Longtime investor Ron Baron's mutual fund has been the the biggest winner over the last five years as his top growth picks reaped outsized returns. The Baron Partners Fund (BPTIX) , with more than $6 billion in assets under management, has notched a five-year total return of 25.7% on an annualized basis, making it the top-performing U.S. equity fund over the period, according to MorningStar. The fund is focused on U.S. companies of any size with significant growth potential. The top holding of the fund by far is Elon Musk 's Tesla, with a 52% portfolio weighting at the end of the third quarter. Baron has been a longtime bull in Tesla . The investor revealed that his firm made over 15 times its investments in Tesla since he first bought the EV stock in 2014, Baron said at the Annual Baron Investment Conference in New York earlier this month. Musk also spoke at the conference. Baron said he believes Tesla will be the largest company in the world in 10 years, and a decade later SpaceX will challenge it for that top spot, he said at the conference. He previously revealed that his biggest purchases this year included $100 million worth of SpaceX private investments. His second biggest holding is CoStar Group , a data and analytics provider for the commercial real estate sector. The company reported 11.6% growth in revenue and a 12.4% increase in net profit for the latest quarter compared with last year. The stock is up 2% this year, outperforming the broader market. CoStar is "armed to the teeth" with a great balance sheet and cash for any acquisitions it will make in the future, according to a note last month from Gordon Haskett. A relatively new holding Baron bought in 2019 is Iridium Communications , a long-time provider of satellite communications to specialized phones. Iridium expects to finalize a contract with a smartphone partner for a direct-to-smartphone service by the end of this year. Baron's top holdings also include insurance company Arch Capital Group , Charles Schwab , FactSet Research and Hyatt Hotels . The veteran investor shared that his foundational way of investing entails finding companies with great leadership and competitive advantage, he said at the conference this month. During this summer's big market rout, when stocks fell into a bear market on fears of a recession, Baron told CNBC that investors were being presented with a once-in-a-lifetime buying opportunity.