Owning berkshire means owning a slice of a huge conglomerate of profitable, growing businesses.  Owning bitcoin means owning an electronic numerical value that's guaranteed by the network.

Berkshire is a productive asset, bitcoin is effectively an e-commodity.  There is virtually no intrinsic value in bitcoin (it doesn't generate massive amounts of value for society).  Owning berkshire for long periods of time is investing (long-term profit and value growth), while owning bitcoin for long periods of time is speculating (believing the next sucker will buy a non-productive asset at a higher price than you).