How to customize the item template in an unbound Xamarin.Forms TreeView (SfTreeView)

<syncfusion:SfTreeView x:Name="treeView">
    <syncfusion:SfTreeView.ItemTemplate>
        <DataTemplate>
            <Grid>
                <Label Text="{Binding Content}" TextColor="{Binding Level, Converter={StaticResource textColorConverter}}" VerticalOptions="Center"/>
            </Grid>
        </DataTemplate>
    </syncfusion:SfTreeView.ItemTemplate>
 
    <syncfusion:SfTreeView.Nodes>
        <treeviewengine:TreeViewNode Content="Australia" IsExpanded="True">
            <treeviewengine:TreeViewNode.ChildNodes>
                <treeviewengine:TreeViewNode Content="New South Wales">
                    <treeviewengine:TreeViewNode.ChildNodes>
                        <treeviewengine:TreeViewNode Content="Sydney"/>
                        <treeviewengine:TreeViewNode Content="Canberra"/>
                        <treeviewengine:TreeViewNode Content="Newcastle–Maitland"/>
                    </treeviewengine:TreeViewNode.ChildNodes>
                </treeviewengine:TreeViewNode>
            </treeviewengine:TreeViewNode.ChildNodes>
        </treeviewengine:TreeViewNode>
    </syncfusion:SfTreeView.Nodes>
</syncfusion:SfTreeView>

public class TextColorConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var level = (int)value;
        if (level == 0) return Color.Red;
        else if (level == 1) return Color.Blue;
        else return Color.Green;
    }
 
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}