can i insert data in subform by insert expression

Hi,

I have a Form "Create_Invoice" with sub form "Product_Details".
I want to insert data into the by a Create_Invoice data which ID I have given.

I use following codes:

invs = Create_Invoice [ID == input.invId];

insert into Create_Invoice
        [
            Added_User=invs.Added_User
            Subjects=invs.Subjects
            Itemline_Products_Type=invs.Itemline_Products_Type
            Due_Date=curNewDueDate
            Discount=invs.Discount
            Sub_Total=invs.Sub_Total
            Tax_Codes=invs.Tax_Codes
            Grand_Total=invs.Grand_Total
            Payment_Status="Unpaid"
            Paid_Amount="0".toDecimal()
            Owed_Amount=invs.Grand_Total
            Comments=""
            Product_Details=invs.Product_Details
        ]

Could not save the script. error showed.

Error at line number : 43
Field 'Product_Details' is of type subform and is not supported in insert expression

so can anyone help me that how to insert data in subform by insert expression.

Regards
Hadi