Jeremy Siegel says it's not too late for investors to join the party even with the Dow at 20,000

Investors shouldn't be afraid to jump into the stock market at these levels, according to Jeremy Siegel, professor of finance at the Wharton School, who had been calling for Dow 20,000 since 2014.

On Wednesday, the Dow Jones Industrial average closed at a record price, ending at 20,837. The average is now up more than 10 percent in the past three months.

"Don't be afraid to get in the market. No one can be sure what's going on short term, but I think there are definitely values here for long-term investors," Siegel told CNBC.

PRO members have access to this exclusive interview, which originally appeared on "Closing Bell."