<DataTemplate x:Key="FolderTemplate" x:DataType="localdata:FolderInfo">
        <TreeViewItem ItemsSource="{x:Bind subFolders}">
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="#Folder#" />
                <Image Width="20" Source="Assets/img2.png"/>
                <TextBlock Text="{x:Bind  FolderName }" />
            </StackPanel>
        </TreeViewItem>
    </DataTemplate>

    <DataTemplate x:Key="FileTemplate" x:DataType="localdata:FolderInfo">
        <TreeViewItem>
            <StackPanel Orientation="Horizontal">
                <Image Width="20" Source="Assets/img3.png"/>
                <TextBlock Text="{x:Bind FolderName}"/>
            </StackPanel>
        </TreeViewItem>
    </DataTemplate>


    <localdata:ExplorerItemTemplateSelector
        x:Key="ExplorerItemTemplateSelector"
        FolderTemplate="{StaticResource FolderTemplate}"
        FileTemplate="{StaticResource FileTemplate}" />

<TreeView
        x:Name="treeview" Grid.Row="2" ItemsSource="{Binding storageFolders,Mode=OneWay}"
        Style="{StaticResource TreeViewStyle1}"

        >
            <TreeView.ItemTemplate>
                <DataTemplate x:DataType="localdata:FolderInfo">
                    <TreeViewItem ItemsSource="{x:Bind subFolders}" Content="{x:Bind FolderName}"/>
                </DataTemplate>
            </TreeView.ItemTemplate>
        </TreeView>

public class ExplorerItemTemplateSelector : DataTemplateSelector
{
    public DataTemplate FolderTemplate { get; set; }
    public DataTemplate FileTemplate { get; set; }

    protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
    {
        var explorerItem = (FolderInfo)item;
        if (explorerItem.IsFolder == true) return FolderTemplate;

        return FileTemplate;
    }
}