How to add nodes to bound mode TreeView in Xamarin.Forms (SfTreeView)

You can add nodes at runtime to bound mode SfTreeView in Xamarin.Forms by updating the bound collection from ViewModel.

You can also refer the following article.

https://www.syncfusion.com/kb/11487/how-to-add-nodes-to-bound-mode-treeview-in-xamarin-forms-sftreeview

ViewModel bound collection updated in OnAddItem handler.

public class FileManagerViewModel
{
    public Command OnAddItem { get; set; }
 
    public FileManagerViewModel()
    {
        GenerateSource();
        OnAddItem = new Command(OnAddItemMethod);
    }
    private void OnAddItemMethod(object obj)
    {
        Assembly assembly = typeof(MainPage).GetTypeInfo().Assembly;
        var game = new FileManager() { ItemName = "Game", ImageIcon = ImageSource.FromResource("TreeViewXamarin.Icons.treeview_folder.png", assembly) };
        var games = new FileManager() { ItemName = "Pubg.exe", ImageIcon = ImageSource.FromResource("TreeViewXamarin.Icons.treeview_exe.png", assembly) };
        game.SubFiles = new ObservableCollection<FileManager>
        {
            games
        };
        ImageNodeInfo.Add(game);
    }
}

XAML

ViewModel command bound to view to add item.

<ContentPage.Content>
    <StackLayout Orientation="Vertical" Padding="5">
        <Button Text="Add Items" x:Name="addItem" HorizontalOptions="Fill" BackgroundColor="Blue" Command="{Binding OnAddItem}" />
        <syncfusion:SfTreeView x:Name="treeView" NotificationSubscriptionMode="CollectionChange,PropertyChange"  
                                ItemHeight="40"
                                Indentation="15"
                                ExpanderWidth="40"
                                ChildPropertyName="SubFiles"
                                ItemsSource="{Binding ImageNodeInfo}"
                                AutoExpandMode="AllNodesExpanded">
            <syncfusion:SfTreeView.ItemTemplate>
                <DataTemplate>
                    <ViewCell>
                        <ViewCell.View>
                            <Grid x:Name="grid" RowSpacing="0" BackgroundColor="Transparent">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="*" />
                                    <RowDefinition Height="1" />
                                </Grid.RowDefinitions>
                                <Grid RowSpacing="0" Grid.Row="0">
                                    <Grid.ColumnDefinitions>
                                        <ColumnDefinition Width="40" />
                                        <ColumnDefinition Width="*" />
                                    </Grid.ColumnDefinitions>
                                    <Grid Padding="5,5,5,5">
                                        <Image
                                                Source="{Binding ImageIcon}"
                                                VerticalOptions="Center"
                                                HorizontalOptions="Center"
                                                HeightRequest="35" 
                                                WidthRequest="35"/>
                                    </Grid>
                                    <Grid Grid.Column="1"
                                                RowSpacing="1"
                                                Padding="1,0,0,0"
                                                VerticalOptions="Center">
                                        <Label LineBreakMode="NoWrap" TextColor="Black"
                                                    Text="{Binding ItemName}"
                                                    VerticalTextAlignment="Center">
                                        </Label>
                                    </Grid>
                                </Grid>
                                <StackLayout Grid.Row="1" HeightRequest="1"/>
                            </Grid>
                        </ViewCell.View>
                    </ViewCell>
                </DataTemplate>
            </syncfusion:SfTreeView.ItemTemplate>
        </syncfusion:SfTreeView>
    </StackLayout>
</ContentPage.Content>

SyncfusionExamples/add-nodes-bound-mode-treeview-xamarin

How to add nodes to bound mode TreeView in Xamarin.Forms (SfTreeView)