public class Group : DependencyObject
    {
        public string Name { get; internal set; }
        public ObservableCollection<Group> Groups { get; internal set; }
        public ObservableCollection<Signal> Signals { get; internal set; }
    }

    public class Signal : DependencyObject
    {
        public string Id { get; internal set; }
        public string Name { get; internal set; }
        public string Description { get; internal set; }
        public bool IsSelected { get; set; }
    }

<TreeView ItemsSource="{Binding Root}">
                <TreeView.Resources>
                    <HierarchicalDataTemplate DataType="{x:Type m:Group}" ItemsSource="{Binding Groups}">
                        <Label Content="{Binding Name}" />
                    </HierarchicalDataTemplate>

                    <DataTemplate DataType="{x:Type m:Signal}">
                        <StackPanel Orientation="Horizontal">
                            <CheckBox IsChecked="{Binding IsSelected}" />
                            <Separator Width="3" Height="0" />
                            <TextBlock Text="{Binding Name}"/>
                        </StackPanel>
                    </DataTemplate>
                    
                </TreeView.Resources>
            </TreeView>

public class GroupModel : DependencyObject
    {
        readonly Group _group;
        public IList Items { get; set; }

        public GroupModel(Group group)
        {
            _group = group;
            Items = new ObservableCollection<DependencyObject>();
            if (_group.Groups != null && _group.Groups.Count > 0)
            {
                foreach (var sub_group in _group.Groups)
                    Items.Add(new GroupModel(sub_group));
            }
            if (_group.Signals != null && _group.Signals.Count > 0)
            {
                foreach (var signal in _group.Signals)
                    Items.Add(new SignalModel(signal));
            }
        }

        public override string ToString()
        {
            return _group.Name;
        }

        public string Name { get { return ToString(); } }

        public List<SignalModel> SelectedItems { 
            get 
            {
                List<SignalModel> result = new List<SignalModel>();

                foreach (var item in Items)
                {
                    if (item is GroupModel)
                        result.AddRange((item as GroupModel).SelectedItems);
                    else if (item is SignalModel)
                    {
                        SignalModel s = item as SignalModel;
                        if (s.IsSelect == true)
                            result.Add(s);
                    }
                }

                return result;
            } 
        }
    }

<TreeView ItemsSource="{Binding Root}" Grid.Row="0">
                <TreeView.Resources>
                    <HierarchicalDataTemplate DataType="{x:Type m:GroupModel}" ItemsSource="{Binding Items}">
                            <Label Content="{Binding Name}" />
                    </HierarchicalDataTemplate>

                    <DataTemplate DataType="{x:Type m:SignalModel}">
                        <StackPanel Orientation="Horizontal">
                            <CheckBox IsChecked="{Binding IsSelected}" />
                            <Separator Width="3" Height="0" />
                            <TextBlock Text="{Binding}"/>
                        </StackPanel>
                    </DataTemplate>
                    
                </TreeView.Resources>
            </TreeView>