I treat these just like stocks, this is an example. I have to prepend "B" to the cusip number for these.
2022-05-01 commodity B91282CBA8
2022-05-01 open Assets:Brokers:Etrade:B91282CBA8 B91282CBA8
2022-05-01 open Income:Interest:Etrade:B91282CBA8 USD
2022-05-01 open Income:Capital-Gains:Etrade:B91282CBA8 USD
2022-12-02 * "buystock" "[B91282CBA8] US Treasury"
Assets:Brokers:Etrade:B91282CBA8 1000 B91282CBA8 {95.55127 USD}
Assets:Brokers:Etrade:USD -95551.27 USD
2022-12-15 * "INT - UNITED STATES TREASURY NOTE - REG INT ON 100000 BND" "[B91282CBA8] "
Assets:Brokers:Etrade:USD 62.5 USD
Income:Interest:Etrade:B91282CBA8 -62.5 USD
2023-12-15 * "DEPOSIT - US TSY NOTE 012523DE15 REDEMPTION OF MATURED BOND"
Assets:Brokers:Etrade:Cash 100000 USD
Assets:Brokers:Etrade:B91282CBA8 -1000 B91282CBA8 {95.55127 USD} @ 100 USD
Income:Capital-Gains:Etrade:B91282CBA8