While inserting multiple rows into a database table, smartest approach is to use bulk copy mechanism. .NET framework has SqlBulkCopy class to copy the rows in bulk to a sql server database table. Following script will be useful in the scenario.

public static void bulkCopyIntoTable(DataTable dtData,string sDatabaseTableName,string sConnectionString)
        {

            using (SqlBulkCopy bulkCopy = new SqlBulkCopy(sConnectionString))
            {
                bulkCopy.DestinationTableName = sDatabaseTableName;
                try
                {
                    // Write from the source to the destination.
                    bulkCopy.WriteToServer(dtData);
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
                finally
                {

                }
            }
        }