UWP TreeViewItem as WrapPanel

Question

 <DataTemplate x:Key="Group" x:DataType="model:GroupedTemplates">
        <muxc:TreeViewItem ItemsSource="{Binding Projects}" >
            <muxc:TreeViewItem.Content>
                <TextBlock>
            <Run Text="Pictures:"/>
            <Run Text="{Binding CountOfPhotos}"/>
                </TextBlock>
            </muxc:TreeViewItem.Content>
        </muxc:TreeViewItem>
    </DataTemplate>
    <DataTemplate x:Key="Template" x:DataType="model:Project">
        <Button Command="{Binding ElementName=Page, 
                                Path=DataContext.TemplateClickCommand}"
                                CommandParameter="{Binding}"
                                Content="{Binding PhotoArray,
                Converter={StaticResource FromArrToGridConverter}}"/>
    </DataTemplate>
    <helpers:GroupTemplateSelector
        x:Key="GroupTemplateSelector"
         ProjectTemplate="{StaticResource Template}"
         GroupTemplate="{StaticResource Group}"/>

 <muxc:TreeView 
        ItemsSource="{Binding TemplateCollection}"
        ItemTemplateSelector="{StaticResource GroupTemplateSelector}">
    </muxc:TreeView>

As result, I have TreeView which items just go down like a list : https://i.stack.imgur.com/qZ77A.png

But I need that my elements in every TreeViewItem be in WrapPanel in Horizontal orientation. Could you help me?

What I need like an image