Subtotal Class

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
        xmlns:local="clr-namespace:WatefallChart" 
        xmlns:dxc="http://schemas.devexpress.com/winfx/2008/xaml/charts" 
        x:Class="WatefallChart.MainWindow" 
        mc:Ignorable="d" 
        Title="MainWindow" Height="500" Width="800">
    <Grid>
        <dxc:ChartControl>
            <dxc:XYDiagram2D dxc:WaterfallSeries2D.TotalBarBrush="Gray" 
                             dxc:WaterfallSeries2D.StartBarBrush="LightGray" 
                             dxc:WaterfallSeries2D.SubtotalBarBrush="DarkGray" 
                             dxc:WaterfallSeries2D.ConnectorBrush="Black">
                <dxc:WaterfallSeries2D.ValueOptions>
                    <dxc:WaterfallRelativeValueOptions StartBarValue="30" 
                                                       StartBarLabel="Start Value" 
                                                       ShowTotal="True" 
                                                       TotalLabel="Total">
                        <dxc:WaterfallRelativeValueOptions.Subtotals>
                            <dxc:Subtotal PointIndex="2" Label="Subtotal"/>
                        </dxc:WaterfallRelativeValueOptions.Subtotals>
                    </dxc:WaterfallRelativeValueOptions>
                </dxc:WaterfallSeries2D.ValueOptions>
                <dxc:WaterfallSeries2D DisplayName="Waterfall" 
                                       LabelsVisibility="True" 
                                       DataSource="{Binding}" 
                                       ArgumentScaleType="Qualitative" 
                                       ArgumentDataMember="Argument" 
                                       ValueDataMember="Value" 
                                       RisingBarBrush="#FF92CEB5" 
                                       FallingBarBrush="#FFDA5859">
                    <dxc:WaterfallSeries2D.Model>
                        <dxc:BorderlessSimpleWaterfall2DModel/>
                    </dxc:WaterfallSeries2D.Model>
                </dxc:WaterfallSeries2D>
                <dxc:XYDiagram2D.AxisX>
                    <dxc:AxisX2D TickmarksMinorVisible="False"/>
                </dxc:XYDiagram2D.AxisX>
            </dxc:XYDiagram2D>
        </dxc:ChartControl>
    </Grid>
</Window>

using System.Collections.Generic;
using System.Windows;

namespace WatefallChart {
    /// <summary> 
    /// Interaction logic for MainWindow.xaml 
    /// </summary> 
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
            this.DataContext = DataLoader.GetDataPoints();
        }
    }
    class DataLoader {
        public static List<DataPoint> GetDataPoints() {
            List<DataPoint> list = new List<DataPoint> {
                new DataPoint("November", 20),
                new DataPoint("December", 10),
                new DataPoint("January", -15),
                new DataPoint("February", 10),
                new DataPoint("March", -10)
            };
            return list;
        }
    }
    public class DataPoint {
        public string Argument { get; private set; }
        public double Value { get; private set; }
        public DataPoint(string arg, double val) {
            Argument = arg;
            Value = val;
        }
    }
}

Imports System.Collections.Generic
Imports System.Windows
Namespace WatefallChart
    Public Partial Class MainWindow
        Inherits Window
        Public Sub New()
            InitializeComponent()
            Me.DataContext = DataLoader.GetDataPoints()
        End Sub 
    End Class 
    Class DataLoader
        Public Shared Function GetDataPoints() As List(Of DataPoint)
            Dim list As List(Of DataPoint) = New List(Of DataPoint) From {
                New DataPoint("November", 20),
                New DataPoint("December", 10),
                New DataPoint("January", -15),
                New DataPoint("February", 10),
                New DataPoint("March", -10)
            }
            Return list
        End Function 
    End Class 
    Public Class DataPoint
        Public Property Argument As String 
        Public Property Value As Double 
        Public Sub New(ByVal arg As String, ByVal val As Double)
            Argument = arg
            Value = val
        End Sub 
    End Class 
End Namespace