[Browsable(false)]
public IList SelectedItems { get; }

<Browsable(False)>
Public ReadOnly Property SelectedItems As IList

public HeatmapSelection() {
    InitializeComponent();
    List<ProductSale> data = LoadData();
    HeatmapDataAdapter.DataSource = data;
    HeatmapDataAdapter.XArgumentComparer = new OriginalOrderComparer();
    heatmapControl1.SelectedItems.Add(data[0]);
}
List<ProductSale> LoadData() {
    List<ProductSale> data = new List<ProductSale>();
    try {
        XDocument sales_xml = XDocument.Load(Utils.GetRelativePath("ProductSales.xml"));
        foreach (XElement monthSale in sales_xml.Root.Elements()) {
            string product = monthSale.Element("Product").Value;
            string month = monthSale.Element("Month").Value;
            List<DailySale> dailySales = new List<DailySale>();
            foreach (XElement daySale in monthSale.Elements("SalesByDay").Elements("DailySale")) {
                dailySales.Add(new DailySale() {
                    Product = product,
                    Date = Convert.ToDateTime(daySale.Element("Date").Value),
                    Revenue = Convert.ToDouble(daySale.Element("Revenue").Value)
                });
            }
            data.Add(new ProductSale() { SalesByDay = dailySales });
        }
    }
    catch {
    }
    return data;
}
void heatmapControl1_SelectedItemsChanged(object sender, XtraCharts.SelectedItemsChangedEventArgs e) {
    List<DailySale> list = new List<DailySale>();
    foreach (ProductSale item in heatmapControl1.SelectedItems)
        list.AddRange(item.SalesByDay);
    chartControl1.DataSource = list;
}

Public Sub New()
    Me.InitializeComponent()
    Dim data As System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.ProductSale) = Me.LoadData()
    Me.HeatmapDataAdapter.DataSource = data
    Me.HeatmapDataAdapter.XArgumentComparer = New DevExpress.XtraTreeMap.Demos.OriginalOrderComparer()
    Me.heatmapControl1.SelectedItems.Add(data(0))
End Sub
Private Function LoadData() As List(Of DevExpress.XtraTreeMap.Demos.ProductSale)
    Dim data As System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.ProductSale) = New System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.ProductSale)()
    Try
        Dim sales_xml As System.Xml.Linq.XDocument = System.Xml.Linq.XDocument.Load(DevExpress.XtraTreeMap.Demos.Utils.GetRelativePath("ProductSales.xml"))
        For Each monthSale As System.Xml.Linq.XElement In sales_xml.Root.Elements()
            Dim product As String = monthSale.Element(CType(("Product"), System.Xml.Linq.XName)).Value
            Dim month As String = monthSale.Element(CType(("Month"), System.Xml.Linq.XName)).Value
            Dim dailySales As System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.DailySale) = New System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.DailySale)()
            For Each daySale As System.Xml.Linq.XElement In monthSale.Elements("SalesByDay").Elements("DailySale")
                dailySales.Add(New DevExpress.XtraTreeMap.Demos.DailySale() With {.Product = product, .[Date] = System.Convert.ToDateTime(daySale.Element(CType(("Date"), System.Xml.Linq.XName)).Value), .Reve
            Next

            data.Add(New DevExpress.XtraTreeMap.Demos.ProductSale() With {.SalesByDay = dailySales})
        Next
    Catch
    End Try
    Return data
End Function

Private Sub heatmapControl1_SelectedItemsChanged(ByVal sender As Object, ByVal e As DevExpress.XtraCharts.SelectedItemsChangedEventArgs)
    Dim list As System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.DailySale) = New System.Collections.Generic.List(Of DevExpress.XtraTreeMap.Demos.DailySale)()
    For Each item As DevExpress.XtraTreeMap.Demos.ProductSale In Me.heatmapControl1.SelectedItems
        list.AddRange(item.SalesByDay)
    Next
    Me.chartControl1.DataSource = list
End Sub