How to load more items in upward direction manually using button click?

<sync:SfListView x:Name="ListView"  IsBusy="True"
            ItemTemplate="{StaticResource MessageTemplateSelector}" 
            ItemsSource="{Binding Messages}"
            ItemSize="100">
            <sync:SfListView.HeaderTemplate>
                <DataTemplate>
                    <ViewCell>
                        <Grid>
                            <Grid BackgroundColor="#d3d3d3" IsVisible="{Binding GridIsVisible}">
                                <Button Text="Load More" Clicked="Button_Clicked" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand"/>
                            </Grid>
                            <sync:LoadMoreIndicator Color="Red" IsRunning="True" IsVisible="{Binding IndicatorIsVisible}"/>
                        </Grid>
                    </ViewCell>
                </DataTemplate>
            </sync:SfListView.HeaderTemplate>
</sync:SfListView>

public partial class MainPage : ContentPage
    {
        MainPageViewModel ViewModel;
        VisualContainer visualContainer;
 
        public MainPage()
        {
            InitializeComponent();
            ViewModel = new MainPageViewModel();
            BindingContext = ViewModel;
            ViewModel.ListView = this.ListView;
            ListView.Loaded += ListView_Loaded;
            visualContainer = ListView.GetVisualContainer();
        }
 
        private void ListView_Loaded(object sender, Syncfusion.ListView.XForms.ListViewLoadedEventArgs e)
        {
            (ListView.LayoutManager as LinearLayout).ScrollToRowIndex(ViewModel.Messages.Count - 1, true);
        }
 
        private async void Button_Clicked(object sender, EventArgs e)
        {
            //To get the current first item which is visible in the View.
            var firstItem = ListView.DataSource.DisplayItems[0];
            ViewModel.GridIsVisible = false;
            ViewModel.IndicatorIsVisible = true;
            await Task.Delay(2000);
            var r = new Random();
 
            //To avoid layout calls for arranging each and every items to be added in the View. 
            ListView.DataSource.BeginInit();
            for (int i = 0; i < 5; i++)
            {
                var collection = new Message();
                collection.Text = ViewModel.MessageText[r.Next(0, ViewModel.MessageText.Count() - 1)];
                collection.IsIncoming = i % 2 == 0 ? true : false;
                collection.MessagDateTime = DateTime.Now.ToString();
                ViewModel.Messages.Insert(0, collection);
            }
            ListView.DataSource.EndInit();
            var firstItemIndex = ListView.DataSource.DisplayItems.IndexOf(firstItem);
            var header = (ListView.HeaderTemplate != null && !ListView.IsStickyHeader) ? 1 : 0;
            var totalItems = firstItemIndex + header;            //Need to scroll back to previous position else the ScrollViewer moves to top of the list.
            ListView.LayoutManager.ScrollToRowIndex(totalItems, true);
            ViewModel.GridIsVisible = true;
            ViewModel.IndicatorIsVisible = false;
        }
    }