Problem with selectable drop-down C #

I have a ComboBox dropdown to call it in some way ( System.Windows.Forms.ComboBox ) in which, I simply invoke the class method to load the data of the bd, the thing is that I have to add a field so that show me all the options that the drop-down has. And I do not know how to do it.

public FormSumatorio()
{
    InitializeComponent();

    List<Tienda> t_list = Tiendas.getTiendas();

    foreach (Tienda t in t_list)
    {
        cBTiendas1.Items.Add(t);
    }
    cBTiendas1.SelectedIndex = 0;
    //cBUnidades.SelectedIndex = 1;
}

GetTiendas Method:

public static List<Tienda> getTiendas()
        {
            List<Tienda> tiendas = new List<Tienda>();

            string sql = "SELECT * FROM tiendas ";

            MySqlCommand cmd = new MySqlCommand(sql);
            MySqlDataReader reader = QueryPSDatabase(cmd);

            if (reader.HasRows)
            {
                while (reader.Read())
                {
                    Tienda t = new Tienda();
                    t.id_store = reader.GetString("id_store");
                    t.ref_tienda = reader.GetString("ref_tienda");
                    t.id_country = reader.GetString("id_country");
                    t.id_state = reader.GetString("id_state");
                    t.name = reader.GetString("name");
                    t.address1 = reader.GetString("address1");
                    t.address2 = reader.GetString("address2");
                    t.city = reader.GetString("city");
                    t.postcode = reader.GetString("postcode");
                    t.transportista = reader.GetString("id_transportista");

                    tiendas.Add(t);
                }
            }
            reader.Close();
            reader.Dispose();
            return tiendas;
        }

After obtaining all the stores, I call the method by clicking the button, in which I pass the argument of the store and I do another query to the bd to obtain all shipments according to the store, with which I would like to have a option that was to see everything. Obviously this list is included in a datagrid.

And the method that loads the info in the ComboBox simply makes the query to mysql and I put everything in a list to send it to the form. With which I wanted to know how I could add an option manually (already with the query I have no problem)

Thanks in advance and regards.