BlackRock Inc.’s iShares Bitcoin Trust has become the world’s largest fund for the original cryptocurrency, amassing almost $20 billion in total assets since listing in the US at the start of the year.The exchange-traded fund held $19.68 billion of the token Tuesday, dethroning the $19.65 billion Grayscale Bitcoin Trust, data compiled by Bloomberg show. The third largest is the $11.1 billion offering from Fidelity Investments....