public IEnumerable DataSource { get; set; }

Public Property DataSource As IEnumerable

public interface INameable {
    string Name { get; }
}

public sealed class DevAVBranch: INameable {
    public string Name { get; set; }
    public List<DevAVProductCategory> Categories { get; set; }
    public double TotalIncome { get => Categories.Sum(c => c.TotalIncome); }
}

public sealed class DevAVProductCategory: INameable {
    public string Name { get; set; }
    public List<DevAVProduct> Products { get; set; }
    public double TotalIncome { get => Products.Sum(p => p.TotalIncome); }
}

public sealed class DevAVProduct: INameable {
    public string Name { get; set; }
    public List<DevAVMonthlyIncome> Sales { get; set; }
    public double TotalIncome { get => Sales.Sum(s => s.Income); }
}

public class DevAVMonthlyIncome {
    public DateTime Month { get; set; }
    public double Income { get; set; }
}

Public Interface INameable
    ReadOnly Property Name As String
End Interface

Public Class DevAVBranch
    Implements INameable

    Public Property Name As String Implements INameable.Name
    Public Property Categories As List(Of DevAVProductCategory)
    Public ReadOnly Property TotalIncome As Double
        Get
            Return Categories.Sum(Function(c) c.TotalIncome)
        End Get
    End Property
End Class

Public Class DevAVProductCategory
    Implements INameable

    Public Property Name As String Implements INameable.Name
    Public Property Products As List(Of DevAVProduct)
    Public ReadOnly Property TotalIncome As Double
        Get
            Return Products.Sum(Function(p) p.TotalIncome)
        End Get
    End Property
End Class

Public Class DevAVProduct
    Implements INameable

    Public Property Name As String Implements INameable.Name
    Public Property Sales As List(Of DevAVMonthlyIncome)
    Public ReadOnly Property TotalIncome As Double
        Get
            Return Sales.Sum(Function(s) s.Income)
        End Get
    End Property
End Class

Public Class DevAVMonthlyIncome
    Public Property Month As DateTime
    Public Property Income As Double
End Class

class MainViewModel {
    public IReadOnlyList<DevAVBranch> Branches { get; } 

    public MainViewModel() {
        Branches = new BranchDAO().GetBranches();
    }
}

Class MainViewModel
    Private _branches As IReadOnlyList(Of DevAVBranch)
    Public ReadOnly Property Branches As IReadOnlyList(Of DevAVBranch)
        Get
            Return _branches
        End Get
    End Property

    Public Sub New()
        _branches = new BranchDAO().GetBranches();
    End Sub
End Class

<Window.DataContext>
    <local:MainViewModel/>
</Window.DataContext>
<Window.Resources>
    <!-- Other resources are here. -->
    <local:DevAVSeriesTemplateSelector
        x:Key="seriesTemplateSelector"
        AllCategoriesTemplate="{StaticResource stackedBarTemplate}"
        BranchCategoriesTemplate="{StaticResource barTemplate}"
        CategoryProductsTemplate="{StaticResource stackedSplineAreaTemplate}"
        ProductTemplate="{StaticResource splineTemplate}">
    </local:DevAVSeriesTemplateSelector>
    <local:DevAVSeriesChildrenSelector x:Key="childrenSelector"/>
    <local:DevAVBreadcrumbTextProvider x:Key="textProvider"/>
<Window.Resources>
<dxc:ChartControl>
    <dxc:XYDiagram2D
        x:Name="diagram" 
        SeriesItemTemplateSelector="{StaticResource seriesTemplateSelector}" 
        DrillDownStateChanged="XYDiagram2D_DrillDownStateChanged">
        <dxc:XYDiagram.SeriesItemsSource>
            <dxc:HierarchicalDataAdapter 
                DataSource="{Binding Branches}"
                ChildrenSelector="{StaticResource childrenSelector}"
                BreadcrumbTextProvider="{StaticResource textProvider}"/>
        </dxc:XYDiagram.SeriesItemsSource>
    </dxc:XYDiagram2D>
<!-- Other Chart Settings.-->
</dxc:ChartControl>

class MainWindow: Window {
    public MainWindow() {
        InitializeComponent()
    }
    private void OnDrillDownStateChanged(object sender, DrillDownStateChangedEventArgs e) {
        diagram.Rotated = e.BreadcrumbItems.Last().IsHome;
    }
}

private void OnDrillDownStateChanged(object sender, DrillDownStateChangedEventArgs e) {
    diagram.Rotated = e.BreadcrumbItems.Last().IsHome;
}

class DevAVSeriesChildrenSelector : IChildrenSelector {
    public IEnumerable SelectChildren(object item) {
        if (item as DevAVBranch branch) return new List<DevAVBranch> { branch };
        if (item as DevAVProductCategory category) return category.Products;
        if (item as DevAVProduct product) return new List<DevAVProduct> { product };
        return null;
    }
}

class DevAVSeriesTemplateSelector : DataTemplateSelector {
    public DataTemplate AllCategoriesTemplate { get; set; }
    public DataTemplate BranchCategoriesTemplate { get; set; }
    public DataTemplate CategoryProductsTemplate { get; set; }
    public DataTemplate ProductTemplate { get; set; }

    public override DataTemplate SelectTemplate(object item, DependencyObject container) {
        Diagram diagram = (Diagram)container;
        if (item is DevAVBranch && diagram.BreadcrumbItems.Count == 1)
            return AllCategoriesTemplate;
        if (item is DevAVBranch)
            return BranchCategoriesTemplate;
        if (item is DevAVProduct && diagram.BreadcrumbItems[diagram.BreadcrumbItems.Count - 1].SourceObject is DevAVProduct)
            return ProductTemplate;
        if (item is DevAVProduct) 
            return CategoryProductsTemplate;
        return null;
    }
}

class DevAVBreadcrumbTextProvider : IBreadcrumbTextProvider {
    public string GetText(object seriesSourceObj, object pointSourceObj) {
        StringBuilder sb = new StringBuilder("(");
        if (seriesSourceObj != null) sb.Append(GetName(seriesSourceObj));
        if (seriesSourceObj != null && pointSourceObj != null) sb.Append(", ");
        if (pointSourceObj != null) sb.Append(GetName(pointSourceObj));
        sb.Append(")");
        return sb.ToString();
    }

    private string GetName(object obj) {
        if (obj is INameable nameable) return nameable.Name;
        return String.Empty;
    }
}

Public Class MainWindow
    Private Sub Diagram_DrillDownStateChanged(sender As Object, e As DrillDownStateChangedEventArgs)
        diagram.Rotated = e.BreadcrumbItems.Last().IsHome
    End Sub
End Class

Public Class DevAVSeriesChildrenSelector
    Implements IChildrenSelector

    Public Function SelectChildren(item As Object) As IEnumerable Implements IChildrenSelector.SelectChildren
        Dim branch = TryCast(item, DevAVBranch)
        If (branch IsNot Nothing) Then Return New List(Of DevAVBranch) From { branch }

        Dim category = TryCast(item, DevAVProductCategory)
        If (category IsNot Nothing) Then Return category.Products

        Dim product = TryCast(item, DevAVProduct)
        If (product IsNot Nothing) Then Return New List(Of DevAVProduct) From { product }

        Return Nothing
    End Function
End Class

Class DevAVSeriesTemplateSelector
    Inherits DataTemplateSelector

    Public Property AllCategoriesTemplate As DataTemplate
    Public Property BranchCategoriesTemplate As DataTemplate
    Public Property CategoryProductsTemplate As DataTemplate
    Public Property ProductTemplate As DataTemplate

    Public Overrides Function SelectTemplate(item As Object, container As DependencyObject) As DataTemplate
        Dim diagram = CType(container, Diagram)

        Dim branch = TryCast(item, DevAVBranch)
        If (branch IsNot Nothing) And (diagram.BreadcrumbItems.Count = 1) Then Return AllCategoriesTemplate
        If (branch IsNot Nothing) Then Return BranchCategoriesTemplate

        Dim product = TryCast(item, DevAVProduct)
        Dim lastLevelSourceProduct = TryCast(diagram.BreadcrumbItems(diagram.BreadcrumbItems.Count - 1).SourceObject, DevAVProduct)
        If (product IsNot Nothing) And (lastLevelSourceProduct IsNot Nothing) Then Return ProductTemplate
        If (product IsNot Nothing) Then Return CategoryProductsTemplate

        Return Nothing
    End Function
End Class

Public Class DevAVBreadcrumbTextProvider
    Implements IBreadcrumbTextProvider
    Public Function GetText(seriesSourceObj As Object, pointSourceObj As Object) As String Implements IBreadcrumbTextProvider.GetText
        Dim sb = New StringBuilder("(")
        If (seriesSourceObj IsNot Nothing) Then sb.Append(GetName(seriesSourceObj))
        If (seriesSourceObj IsNot Nothing And pointSourceObj IsNot Nothing) Then sb.Append(", ")
        If (pointSourceObj IsNot Nothing) Then sb.Append(GetName(pointSourceObj))
        sb.Append(")")
        Return sb.ToString()
    End Function

    Private Function GetName(obj As Object) As String
        Dim nameable = TryCast(obj, INameable)
        If (nameable IsNot Nothing) Then Return nameable.Name
        Return String.Empty
    End Function
End Class