The default index 0 is getting selected in ASP.Net DropDownList

The provided method is for filling the data in dropdown list. first the selected index of dropdown is -1 but after Databind() method line the the selected index becomes 0 and first item of the list gets selected by default i tried to set selected index to -1 or clearSelections but its not being set

if i try to add the first value like select at 0th index. the select item is getting inserted in 0th index but then the selected index becoming 1 after adding data and again the first item of list is getting selected

ListItem defaultItem = new ListItem("Select", "");
cmbCountry.Items.Insert(0, defaultItem);

I am calling this function on page load so i checked like this on page_load event

<asp:DropDownList ID="cmbCountry" runat="server" CssClass=" custom-dropdown" 
    AppendDataBoundItems="false" EnableViewState="False" AutoPostBack="true" 
    ViewStateMode="Enabled"></asp:DropDownList>

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        Fill_Country();
    }
}

protected void Fill_Country()
{
    DataSet ds = new DataSet();
    ds = FunctionClass.ExecuteStoredProcedure("Fill_CountryName");
    if (ds.Tables.Count > 0)
    {
        if (ds.Tables[0].Rows.Count > 0)
        {
            int i = cmbCountry.SelectedIndex;

            cmbCountry.DataSource = ds.Tables[0];
            cmbCountry.DataTextField = "Country";
            cmbCountry.DataValueField = "Id";
            cmbCountry.DataBind();
            ListItem defaultItem = new ListItem("Select", "");
            cmbCountry.Items.Insert(0, defaultItem);
            cmbCountry.SelectedIndex = -1;
        }
        else
        {
            cmbCountry.DataSource = null;
            cmbCountry.DataBind();//enter code here
        }
    }
}