Parent Company Stock Accounted for by Subsidiary as Investment Securities

If company X owns 100% of Company Y , and then company Y invested in the stocks of company X “the investment is immaterial almost 0.01%” , how will it be accounted in Y books and how will it be treated in the consolidation, the investment will not lose the control of Company X on Company Y

shall the stocks be treated as treasury stocks , also they purchased the stock at fair market value so what will be the entries and the correct accounting treatment.