Try this, i have tried it and working well
List<Products> result1 = new List<Products>();
Products obj = new Products();
obj.ProdID = 0;
obj.Product_Name= "Select";
result1.Add(obj);
result1.AddRange(myData);
comboBox1.ItemsSource = result1;
comboBox1.DisplayMemberPath = "Product_Name";
comboBox1.SelectedValuePath = "Product_Name";
comboBox1.SelectedValue = "ProdID";
comboBox1.SelectedIndex = 0;