if (!Page.IsPostBack)
{
using (SPSite site = new ("http://SP2013"))
{
using (SPWeb web = site.OpenWeb())
{
SPList list = web.Lists["NameOfYourList"];
dropSite.DataSource = list.Items;
dropSite.DataValueField = "Title";
dropSite.DataTextField = "Title";
dropSite.DataBind();
}
}
}