Insert Data to Table MultiSelect Field

1

How to add data to MultiSelect in doc type that have Table MultiSelect Field using frappe?

2 
if(frm.doc.__islocal){
            var new_row = frm.add_child("table_fieldname");
                new_row.fieldname_in_childtable = "Test 1";
                frm.refresh_field("table_fieldname");
        }