insert excel sheet to database , prevent data from being inserted multiple times causing dupliacates

i am inserting excel sheet to database using datatables and OLEDB , the sheets have different names so i am using a data table to check for sheet names and select data from them ,the problem is the data gets inserted multiple times when the loop runs causing duplicates. i would like the data to be inserted once but I'm not sure how to implement that on the code. Would appreciate the help, here's my code : 

public void up(string sFileName = @"filename")
        { 
        string ssqltable = "[dbo].[PB]";
        //string sFileName = @"filename";

    try{
        string sConStr = string.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 8.0;HDR=YES';", sFileName);
        DataTable dt = new DataTable();
        SqlConnection sqlconn = new SqlConnection(strConnString);

         sqlconn.Open();
        using (OleDbConnection connection = new OleDbConnection(sConStr))
        {
            connection.Open();
           dt = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, new object[] { null, null, null, "TABLE" });
           var sheets = dt.Rows[0].Field<string>("TABLE_NAME");
            foreach(var sheet in sheets) //loop through the collection of sheets ;)
            {
                //your logic here...
                        string myexceldataquery = string.Format("Select * FROM [{0}]; ", sheets);
                        //get data

                        OleDbConnection oledbconn = new OleDbConnection(sConStr);
                        OleDbCommand oledbcmd = new OleDbCommand(myexceldataquery, oledbconn);
                        oledbconn.Open();
                        
                                             
                        OleDbDataReader dr = oledbcmd.ExecuteReader();
                             {
                              //sql bulk copy here!
                                
                                DataTable table = new DataTable("benlist");
                                table.Load(dr);

                                // add two extra columns to data table to be added to database table 
                                table.Columns.Add("Filename",typeof(string));
                                table.Columns.Add("User",typeof(string));

                                //set path
                                string CurrentFilePath = Path.GetFullPath(fuAttachment.PostedFile.FileName);
                                // add data to additional columns
                                foreach (DataRow row in table.Rows){

                                row["Filename"] = Path.GetFileNameWithoutExtension(CurrentFilePath);
                                row["User"] = Session["Username"].ToString();
                }

                Session["filename"] = Path.GetFileNameWithoutExtension(CurrentFilePath);

                SqlBulkCopy bulkcopy = new SqlBulkCopy(strConnString);
                bulkcopy.DestinationTableName = ssqltable;
          
                
                ////Mapping Table column    

                
                bulkcopy.ColumnMappings.Add("ParentId", "[ParentId]");
                bulkcopy.ColumnMappings.Add("PPRDate", "[PPRDate]");
                bulkcopy.ColumnMappings.Add("Caption", "[Caption]");
                bulkcopy.ColumnMappings.Add("Filename","Filename");
                bulkcopy.ColumnMappings.Add("User","User");


                //sqlcmd.ExecuteNonQuery();
            //    while (dr.Read())
            //    {
                    bulkcopy.WriteToServer(table);

            //    }
                connection.Close();
                sqlconn.Close();

                             }
                        
                    }
                }
        
        
            }
            catch (Exception){}
            ClientScript.RegisterStartupScript(GetType(), "alert", "alert('File Uploaded');", true);