multiple pie chart display in rad chart

hi

i want to display multiple value in single pie chart but it gives  multiple pie chart so how to resolve it.

following pei chart and code

  private void BindColorPieChart()
        {
            //DataTable dt = null;
            DataController dc = new DataController();
            DataTable dt = dc.GetUsageDetailsOne(Convert.ToDateTime(txtTodate.Text.Trim()), Convert.ToDateTime(txtFromdate.Text.Trim()));
            if (dt.Rows.Count == 0)
            {
                ColorPieChart.HttpHandlerUrl = ResolveUrl("ChartImage.axd");
                ColorPieChart.Visible = false;
                lblMessage.Text = "No data found";
            }
            else
            {

                ColorPieChart.HttpHandlerUrl = ResolveUrl("ChartImage.axd");
                ColorPieChart.ChartTitle.TextBlock.Text = "Usage Details";
                ColorPieChart.Legend.Appearance.Position.AlignedPosition = Telerik.Charting.Styles.AlignedPositions.TopRight;

                ColorPieChart.PlotArea.XAxis.AxisLabel.Visible = true;
                ColorPieChart.PlotArea.YAxis.AxisLabel.Visible = true;
                ColorPieChart.AutoLayout = true;
                ColorPieChart.Legend.TextBlock.Visible = true;
              
                
                ChartSeries series = new ChartSeries();
                series.Type = ChartSeriesType.Pie;
                series.Appearance.LegendDisplayMode = ChartSeriesLegendDisplayMode.ItemLabels;
                series.DataYColumn = "TotalCost";
                //series.Name = "Total Cost";
     
               series.DataLabelsColumn = "TotalCost";
                series.Appearance.ShowLabelConnectors = true;


             
                ColorPieChart.Series.Add(series);
                ColorPieChart.DataSource = dt;
               

                ColorPieChart.DataBind();
            }
        }
        protected void lnkToDate_Click(object sender, EventArgs e)
        {
            CalToDate.Visible = !CalToDate.Visible;
        }
        protected void lnkFromDate_Click(object sender, EventArgs e)
        {
            CalFromDate.Visible = !CalFromDate.Visible;
        }
        protected void CalToDate_SelectionChanged(object sender, EventArgs e)
        {
            //set date in MM/dd/yyyy format in textbox
            txtTodate.Text = CalToDate.SelectedDate.ToString("MM/dd/yyyy");
            if (txtTodate.Text != string.Empty)
                CalToDate.Visible = false;
        }
        protected void CalFromDate_SelectionChanged(object sender, EventArgs e)
        {
            //set date in MM/dd/yyyy format in textbox
            txtFromdate.Text = CalFromDate.SelectedDate.ToString("MM/dd/yyyy");
            if (txtFromdate.Text != string.Empty)
                CalFromDate.Visible = false;
        }
        protected void btnGo_Click(object sender, EventArgs e)
        {
            ColorPieChart.Visible = true;
            BindColorPieChart();
        }
        protected void RadChart1_ItemDataBound(object sender, Telerik.Charting.ChartItemDataBoundEventArgs e)
        {
            e.SeriesItem.Name = e.SeriesItem.Name = (e.DataItem as DataRowView).Row["TotalCost"].ToString();
        }
    }

UI part aspx

<telerik:RadChart ID="ColorPieChart" runat="server" Height="600px" Width="700px" DefaultType="Pie">
        <ChartTitle>
            <TextBlock Text="">
            </TextBlock>
        </ChartTitle>
    </telerik:RadChart>