how to make data set contain multiple tables?

I have the problem to add multiple tables in 1 data set, I only able to load 1 table in 1 data set. I could not get the customer table and item table in 1 data set. Where did I did wrong? This is my first time to do with C# program

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Linq;
using System.Data;
namespace DataSET
{
    class Program
    {

        static void Main(string[] args)
        {

            GetCustDetail();
            GetItemDetail();
        }
        public static void GetCustDetail()
        {
            DataSet dataSet = new DataSet("Customer");
            dataSet.ReadXml("CustDetail.xml", XmlReadMode.ReadSchema);
            DataTable cust_Table = new DataTable();
            DataColumn cust_Column = cust_Table.Columns.Add("CustID", typeof(Int32));
            cust_Column.AllowDBNull = false;
            cust_Column.Unique = true;
            cust_Table.Columns.Add("CustLName", typeof(String));
            cust_Table.Columns.Add("Purchases", typeof(Double));
            foreach (DataTable dataTable in dataSet.Tables)
                cust_Table.BeginLoadData();
            dataSet.ReadXml("CustDetail.xml");
            foreach (DataTable dataTable in dataSet.Tables)
                cust_Table.EndLoadData();

        }
        public static void GetItemDetail()
        {
            DataSet dataSet = new DataSet();
            dataSet.ReadXml("ItemDetail.xml", XmlReadMode.ReadSchema);
            DataTable item_Table = new DataTable();
            DataColumn item_Column = item_Table.Columns.Add("ItemID", typeof(Int32));
            item_Column.AllowDBNull = false;
            item_Column.Unique = true;
            item_Table.Columns.Add("ItemName", typeof(String));
            item_Table.Columns.Add("Decription", typeof(Double));
            foreach (DataTable dataTable in dataSet.Tables)
                item_Table.BeginLoadData();
            dataSet.ReadXml("ItemDetail.xml");
            foreach (DataTable dataTable in dataSet.Tables)
                item_Table.EndLoadData();
        }


    }
}