Last week's rout erased $1 trillion from U.S. equities amid concern Greek insolvency is inevitable and Europe can't contain the damage. The S&P 500 last week was trading at 12.4 times earnings in the past 12 months, 4.6 percent below its average valuation at the lowest point during the last nine bear markets, according to data compiled by Bloomberg.
"He has a lot of investments in the largest companies in the market, so putting his money in Berkshire is another way of being bullish on the market," said Eric Green, a Philadelphia- based fund manager at Penn Capital Management which oversees about $6 billion, said in a telephone interview. "If the stock market is going down, then his stock will go down, and he's certainly smart enough to know that and he thinks the market is undervalued."