public DetailDescriptorCollection DetailDescriptors { get; }

Public ReadOnly Property DetailDescriptors As DetailDescriptorCollection

using DevExpress.Xpf.Grid;
using System.Windows;

namespace MasterDetailInCode {
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
            GridControl gridControl = CreateGridControl();
            AddDetails(gridControl);
            gridControl.Loaded += (d, e) => { (d as GridControl)?.ExpandMasterRow(0); };
            grid.Children.Add(gridControl);
        }

        private GridControl CreateGridControl() {
            GridControl gridControl = new GridControl();
            gridControl.AutoGenerateColumns = AutoGenerateColumnsMode.AddNew;
            gridControl.ItemsSource = Employees.GetEmployees();
            gridControl.View = new TableView();
            ((TableView)gridControl.View).AutoWidth = true;
            ((TableView)gridControl.View).ShowGroupPanel = false;
            gridControl.View.DetailHeaderContent = nameof(Employees);

            return gridControl;
        }
        private void AddDetails(GridControl gridControl) {
            GridControl detailGridControl = new GridControl();
            detailGridControl.AutoGenerateColumns = AutoGenerateColumnsMode.AddNew;
            detailGridControl.View = new TableView();
            ((TableView)detailGridControl.View).AutoWidth = true;
            ((TableView)detailGridControl.View).ShowGroupPanel = false;
            detailGridControl.View.DetailHeaderContent = nameof(Employee.Orders);

            DataControlDetailDescriptor gridDetail = new DataControlDetailDescriptor();
            gridDetail.ItemsSourcePath = nameof(Employee.Orders);
            gridDetail.DataControl = detailGridControl;

            ContentDetailDescriptor customDetail = new ContentDetailDescriptor();
            customDetail.ContentTemplate = (DataTemplate)FindResource("notesTemplate");
            customDetail.HeaderContent = nameof(Employee.Notes);

            ContentDetailDescriptor chartDetail = new ContentDetailDescriptor();
            chartDetail.ContentTemplate = (DataTemplate)FindResource("chartTemplate");
            chartDetail.HeaderContent = "Stats";

            TabViewDetailDescriptor tabDetail = new TabViewDetailDescriptor();
            tabDetail.DetailDescriptors.Add(gridDetail);
            tabDetail.DetailDescriptors.Add(customDetail);
            tabDetail.DetailDescriptors.Add(chartDetail);

            gridControl.DetailDescriptor = tabDetail;
        }
    }
}

Imports DevExpress.Xpf.Grid
Imports System.Windows

Namespace MasterDetailInCode

    Public Partial Class MainWindow
        Inherits Window

        Public Sub New()
            Me.InitializeComponent()
            Dim gridControl As GridControl = CreateGridControl()
            AddDetails(gridControl)
            AddHandler gridControl.Loaded, Sub(d, e) TryCast(d, GridControl)?.ExpandMasterRow(0)
            Me.grid.Children.Add(gridControl)
        End Sub

        Private Function CreateGridControl() As GridControl
            Dim gridControl As GridControl = New GridControl()
            gridControl.AutoGenerateColumns = AutoGenerateColumnsMode.AddNew
            gridControl.ItemsSource = Employees.GetEmployees()
            gridControl.View = New TableView()
            CType(gridControl.View, TableView).AutoWidth = True
            CType(gridControl.View, TableView).ShowGroupPanel = False
            gridControl.View.DetailHeaderContent = NameOf(Employees)
            Return gridControl
        End Function

        Private Sub AddDetails(ByVal gridControl As GridControl)
            Dim detailGridControl As GridControl = New GridControl()
            detailGridControl.AutoGenerateColumns = AutoGenerateColumnsMode.AddNew
            detailGridControl.View = New TableView()
            CType(detailGridControl.View, TableView).AutoWidth = True
            CType(detailGridControl.View, TableView).ShowGroupPanel = False
            detailGridControl.View.DetailHeaderContent = NameOf(Employee.Orders)
            Dim gridDetail As DataControlDetailDescriptor = New DataControlDetailDescriptor()
            gridDetail.ItemsSourcePath = NameOf(Employee.Orders)
            gridDetail.DataControl = detailGridControl
            Dim customDetail As ContentDetailDescriptor = New ContentDetailDescriptor()
            customDetail.ContentTemplate = CType(FindResource("notesTemplate"), DataTemplate)
            customDetail.HeaderContent = NameOf(Employee.Notes)
            Dim chartDetail As ContentDetailDescriptor = New ContentDetailDescriptor()
            chartDetail.ContentTemplate = CType(FindResource("chartTemplate"), DataTemplate)
            chartDetail.HeaderContent = "Stats"
            Dim tabDetail As TabViewDetailDescriptor = New TabViewDetailDescriptor()
            tabDetail.DetailDescriptors.Add(gridDetail)
            tabDetail.DetailDescriptors.Add(customDetail)
            tabDetail.DetailDescriptors.Add(chartDetail)
            gridControl.DetailDescriptor = tabDetail
        End Sub
    End Class
End Namespace

<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:MasterDetailInCode"
        xmlns:dxg="http://schemas.devexpress.com/winfx/2008/xaml/grid" 
        xmlns:dxc="http://schemas.devexpress.com/winfx/2008/xaml/charts"
        x:Class="MasterDetailInCode.MainWindow"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
        <DataTemplate x:Key="notesTemplate">
            <TextBlock Text="{Binding Path=Notes}" TextWrapping="Wrap" Padding="4"/>
        </DataTemplate>
        <DataTemplate x:Key="chartTemplate">
            <dxc:ChartControl DataSource="{Binding Path=Orders}">
                <dxc:SimpleDiagram2D>
                    <dxc:SimpleDiagram2D.Series>
                        <dxc:PieSeries2D ArgumentDataMember="Supplier" ValueDataMember="Quantity" LabelsVisibility="True">
                            <dxc:PieSeries2D.PointOptions>
                                <dxc:PointOptions>
                                    <dxc:PointOptions.ValueNumericOptions>
                                        <dxc:NumericOptions Format="Percent" Precision="0"/>
                                    </dxc:PointOptions.ValueNumericOptions>
                                </dxc:PointOptions>
                            </dxc:PieSeries2D.PointOptions>
                            <dxc:PieSeries2D.LegendPointOptions>
                                <dxc:PointOptions Pattern="{}{A}"/>
                            </dxc:PieSeries2D.LegendPointOptions>
                        </dxc:PieSeries2D>
                    </dxc:SimpleDiagram2D.Series>
                </dxc:SimpleDiagram2D>
                <dxc:ChartControl.Legend>
                    <dxc:Legend Visibility="Visible"/>
                </dxc:ChartControl.Legend>
            </dxc:ChartControl>
        </DataTemplate>
    </Window.Resources>

    <Grid x:Name="grid"/>

</Window>