try with below code :
@Html.DropDownList("ReportId", new SelectList(Test(), "Value", "Text"), "Select Report")
Then try to set dataset to Selectlistitem from below code that is:
public static List<SelectListItem> Test()
{
//Decalre Selectlistitem
var objselectList = new List<SelectListItem>();
//over here set listof value = list of your dataset value
foreach (var objitem in listofvalue)
{
objselectList.Add(new SelectListItem
{
Text = objitem.ReportID,
Value = Convert.ToString(objitem.objitem),
});
}
return objselectList;
}