public static DataSet FirstColumn(string filename)
    {

        string filepath = filename;

        string sheetName = "First";
        //Oledb connection to generate excel in temporary folder on server
        string connectionstring = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" + filepath + "';Extended Properties="Excel 12.0 Xml;HDR=YES;"";
        using (OleDbConnection conn = new OleDbConnection(connectionstring))
        {
            conn.Open();
            OleDbDataAdapter objDA = new System.Data.OleDb.OleDbDataAdapter
            ("select * from [" + sheetName + "$]", conn);
            DataSet excelDataSet = new DataSet();
            objDA.Fill(excelDataSet);
            return excelDataSet;
        }