You might want to pose this question to your financial advisor or broker but, according to the Grayscale tax information statement, GBTC is a grantor trust and:
Shareholders generally will be treated, for U.S. federal income tax purposes, as if they directly owned a pro rata share of the underlying assets held in the Trust.
See https://grayscale.co/wp-content/uploads/2019/02/GBTC-Tax-Info-Letter-2018.pdf
