Buffett's stake in AAPL exceeds 20% of BRK's market value. 

Buffett isnt afraid of running a concentrated portfolio but not sure if this is what he had in mind in terms of allocation

Undervaluation of BRK is a big contributing factor 
$BRK $AAPL   @stig_brodersen @PrestonPysh https://t.co/PCNsIqU4Bh