I am trying to get a `TreeView` to bind my collection so that all groups show nested groups and each group will show entry.

How can I use the `HierarchicalDataTemplate` so that the `TreeView` will process both SubGroups and Entries collection?

Groups show subgroups and entries:

    Example:
    Group1
    --Entry
    --Entry
    Group2
    --Group4
    ----Group1
    ------Entry
    ------Entry
    ----Entry
    ----Entry
    --Entry
    --Entry
    Group3
    --Entry
    --Entry

&lt;br&gt;
&lt;h2&gt;Objects:&lt;/h2&gt;
&lt;hr /&gt;

    namespace TaskManager.Domain
    {
        public class Entry
        {
            public int Key { get; set; }
            public string Name { get; set; }
        }
    }

    namespace TaskManager.Domain
    {
        public class Group
        {
            public int Key { get; set; }
            public string Name { get; set; }
    
            public IList&lt;Group&gt; SubGroups { get; set; }
            public IList&lt;Entry&gt; Entries { get; set; }
        }
    }


&lt;h2&gt;Test data:&lt;/h2&gt;
&lt;hr /&gt;

    namespace DrillDownView
    {
        public class TestData
        {

            public IList&lt;Group&gt; Groups = new List&lt;Group&gt;();

            public void Load()
            {
                Group grp1 = new Group() { Key = 1, Name = &quot;Group 1&quot;, SubGroups = new List&lt;Group&gt;(), Entries = new List&lt;Entry&gt;() };
                Group grp2 = new Group() { Key = 2, Name = &quot;Group 2&quot;, SubGroups = new List&lt;Group&gt;(), Entries = new List&lt;Entry&gt;() };
                Group grp3 = new Group() { Key = 3, Name = &quot;Group 3&quot;, SubGroups = new List&lt;Group&gt;(), Entries = new List&lt;Entry&gt;() };
                Group grp4 = new Group() { Key = 4, Name = &quot;Group 4&quot;, SubGroups = new List&lt;Group&gt;(), Entries = new List&lt;Entry&gt;() };

                //grp1
                grp1.Entries.Add(new Entry() { Key=1, Name=&quot;Entry number 1&quot; });
                grp1.Entries.Add(new Entry() { Key=2, Name=&quot;Entry number 2&quot; });
                grp1.Entries.Add(new Entry() { Key=3,Name=&quot;Entry number 3&quot; });

                //grp2
                grp2.Entries.Add(new Entry(){ Key=4, Name = &quot;Entry number 4&quot;});
                grp2.Entries.Add(new Entry(){ Key=5, Name = &quot;Entry number 5&quot;});
                grp2.Entries.Add(new Entry(){ Key=6, Name = &quot;Entry number 6&quot;});

                //grp3
                grp3.Entries.Add(new Entry(){ Key=7, Name = &quot;Entry number 7&quot;});
                grp3.Entries.Add(new Entry(){ Key=8, Name = &quot;Entry number 8&quot;});
                grp3.Entries.Add(new Entry(){ Key=9, Name = &quot;Entry number 9&quot;});

                //grp4
                grp4.Entries.Add(new Entry(){ Key=10, Name = &quot;Entry number 10&quot;});
                grp4.Entries.Add(new Entry(){ Key=11, Name = &quot;Entry number 11&quot;});
                grp4.Entries.Add(new Entry(){ Key=12, Name = &quot;Entry number 12&quot;});

                grp4.SubGroups.Add(grp1);
                grp2.SubGroups.Add(grp4);

                Groups.Add(grp1);
                Groups.Add(grp2);
                Groups.Add(grp3);
            }
        }
    }

&lt;h2&gt;XAML:&lt;/h2&gt;
&lt;hr /&gt;

    &lt;Window x:Class=&quot;DrillDownView.Window2&quot;
            xmlns=&quot;http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
            xmlns:x=&quot;http://schemas.microsoft.com/winfx/2006/xaml&quot;
            xmlns:local=&quot;clr-namespace:TaskManager.Domain;assembly=TaskManager.Domain&quot;
            Title=&quot;Window2&quot; Height=&quot;300&quot; Width=&quot;300&quot;&gt;
        &lt;Grid&gt;
            &lt;Grid.RowDefinitions&gt;
                &lt;RowDefinition Height=&quot;Auto&quot; /&gt;
            &lt;/Grid.RowDefinitions&gt;
            &lt;Grid.ColumnDefinitions&gt;
                &lt;ColumnDefinition Width=&quot;Auto&quot; /&gt;
            &lt;/Grid.ColumnDefinitions&gt;
       
            &lt;TreeView Name=&quot;GroupView&quot; Grid.Row=&quot;0&quot; Grid.Column=&quot;0&quot; ItemsSource=&quot;{Binding}&quot;&gt;
                &lt;TreeView.Resources&gt;
                    &lt;HierarchicalDataTemplate DataType=&quot;{x:Type local:Group}&quot; ItemsSource=&quot;{Binding SubGroups}&quot;&gt;
                        &lt;TextBlock Text=&quot;{Binding Path=Name}&quot; /&gt;
                    &lt;/HierarchicalDataTemplate&gt;
                    &lt;HierarchicalDataTemplate DataType=&quot;{x:Type local:Entry}&quot; ItemsSource=&quot;{Binding Entries}&quot;&gt;
                        &lt;TextBlock Text=&quot;{Binding Path=Name}&quot; /&gt;
                    &lt;/HierarchicalDataTemplate&gt;
                &lt;/TreeView.Resources&gt;
            &lt;/TreeView&gt;
        &lt;/Grid&gt;
    &lt;/Window&gt;


&lt;h2&gt;XAML.CS:&lt;/h2&gt;
&lt;hr /&gt;

    public partial class Window2 : Window
    {
        public Window2()
        {
            InitializeComponent();
            LoadView();
        }

        private void LoadView()
        {
            TestData data = new TestData();
            data.Load();
            GroupView.ItemsSource = data.Groups;
        }
    }



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WPF TreeView HierarchicalDataTemplate - binding to object with multiple child collections