using System.Collections.Generic;

namespace HierarchicalDataTemplate {

    public class ViewModel {
        public Data MyData { get; set; }
        public object SelectedItem { get; set; }
        public ViewModel() {
            MyData = new Data();
        }
    }
    public class Data {
        public ObservableCollection<Category> Categories { get; set; }
        public Data() {
            Categories = new ObservableCollection<Category>();
            ObservableCollection<Item> subitems = new ObservableCollection<Item>();
            subitems.Add(new Item() { ItemName = "Chair", Description = "A red chair." });
            subitems.Add(new Item() { ItemName = "Table", Description = "An old table." });
            Categories.Add(new Category() { CategoryName = "Furniture", Items = subitems });
            ObservableCollection<Item> books = new ObservableCollection<Item>();
            books.Add(new Item() { ItemName = "Dictionary", Description = "My old French-English Dictionary" });
            Categories.Add(new Category() { CategoryName = "Books", Items = books });
        }
    }
    public class Category {
        public string CategoryName { get; set; }
        public string Description { get; set; }
        public List<Item> Items { get; set; }
    }
    public class Item {
        public string ItemName { get; set; }
        public string Description { get; set; }
    }
}

<dx:DXWindow
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
        xmlns:dxb="http://schemas.devexpress.com/winfx/2008/xaml/bars"
        xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors"
        xmlns:dxa="http://schemas.devexpress.com/winfx/2008/xaml/accordion" 
        xmlns:local="clr-namespace:HierarchicalDataTemplate" 
        x:Class="HierarchicalDataTemplate.MainWindow"
        Title="MainWindow" Height="350" Width="525">
    <dx:DXWindow.DataContext>
        <local:ViewModel/>
    </dx:DXWindow.DataContext>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="1*"/>
            <ColumnDefinition Width="2*"/>
        </Grid.ColumnDefinitions>
        <Border Margin="5" Grid.Column="0" BorderBrush="Black" BorderThickness="1">
            <dxa:AccordionControl x:Name="accordion" SelectionUnit="SubItem" 
                                  ItemsSource="{Binding MyData.Categories }" SelectedItem="{Binding SelectedItem}">
                <dxa:AccordionControl.ItemTemplate>
                    <HierarchicalDataTemplate DataType="{x:Type local:Category}" ItemsSource="{Binding Items}">
                        <TextBlock Text="{Binding CategoryName}"/>
                        <HierarchicalDataTemplate.ItemTemplate>
                            <DataTemplate DataType="{x:Type local:Item}">
                                <TextBlock Text="{Binding ItemName}"/>
                            </DataTemplate>
                        </HierarchicalDataTemplate.ItemTemplate>
                    </HierarchicalDataTemplate>
                </dxa:AccordionControl.ItemTemplate>
            </dxa:AccordionControl>
        </Border>
        <Border Margin="5" Grid.Column="1" BorderBrush="Black" BorderThickness="1">
            <StackPanel>
                <StackPanel Orientation="Horizontal">
                    <Label Margin="5" VerticalAlignment="Center">Item Name</Label>
                    <dxe:TextEdit Margin="5" Width="150" Text="{Binding SelectedItem.Description}"/>
                </StackPanel>
                <StackPanel Orientation="Horizontal">
                    <Button Margin="5" Content="Expand All Items" 
                            Command="{Binding ElementName=accordion, Path=Commands.ExpandAllItems}" />
                    <Button Margin="5" Content="Collapse All Items" 
                            Command="{Binding ElementName=accordion, Path=Commands.CollapseAllItems}" />
                </StackPanel>
            </StackPanel>
        </Border>
    </Grid>
</dx:DXWindow>

Imports System.Collections.Generic
Imports System.Collections.ObjectModel;

Namespace HierarchicalDataTemplate

    Public Class ViewModel
        Public Property MyData() As Data
        Public Property SelectedItem() As Object
        Public Sub New()
            MyData = New Data()
        End Sub
    End Class
    Public Class Data
        Public Property Categories() As ObservableCollectiont(Of Category)
        Public Sub New()
            Categories = New ObservableCollection(Of Category)()
            Dim subitems As New ObservableCollection(Of Item)()
            subitems.Add(New Item() With { _
                .ItemName = "Chair", _
                .Description = "A red chair." _
            })
            subitems.Add(New Item() With { _
                .ItemName = "Table", _
                .Description = "An old table." _
            })
            Categories.Add(New Category() With { _
                .CategoryName = "Furniture", _
                .Items = subitems _
            })
            Dim books As New ObservableCollection(Of Item)()
            books.Add(New Item() With { _
                .ItemName = "Dictionary", _
                .Description = "My old French-English Dictionary" _
            })
            Categories.Add(New Category() With { _
                .CategoryName = "Books", _
                .Items = books _
            })
        End Sub
    End Class
    Public Class Category
        Public Property CategoryName() As String
        Public Property Description() As String
        Public Property Items() As ObservableCollection(Of Item)
    End Class
    Public Class Item
        Public Property ItemName() As String
        Public Property Description() As String
    End Class
End Namespace