What types are allowed in DataSource?

<EjsTreeView TValue="FileInfoViewModel">
    <TreeViewFieldsSettings TValue="FileInfoViewModel"
                            DataSource="@FileInfoViewModels"
                            Id="Key"
                            Text="Name"
                            Child="@("Children")"
                            Selected="Selected"
                            Expanded="Expanded">
    </TreeViewFieldsSettings>
</EjsTreeView>
@code
{
    public ReadOnlyObservableCollection<FileInfoViewModel> FileInfoViewModels;

    private readonly CompositeDisposable cleanup = new CompositeDisposable();

    protected override void OnInitialized()
    {
        base.OnInitialized();

        var tree = FileSystemService.FileInfoTree;
        tree.Bind(out FileInfoViewModels)
            .DisposeMany()
            .Subscribe()
            .DisposeWith(cleanup);
    }

    public void Dispose()
    {
        cleanup.Dispose();
    }
}

public class FileInfoViewModel : ReactiveObject, IDisposable
{
    private readonly CompositeDisposable cleanup = new CompositeDisposable();

    public string Key { get; }
    public string Name => FileInfo.Name;
    public Optional<FileInfoViewModel> Parent { get; }
    public VirtualFileInfo FileInfo { get; }

    [Reactive]
    public bool Expanded { get; set; }
    [Reactive]
    public bool Selected { get; set; }

    private ReadOnlyObservableCollection<FileInfoViewModel> children;
    public ReadOnlyObservableCollection<FileInfoViewModel> Children => children;

    internal FileInfoViewModel(Node<VirtualFileInfo, string> node, FileInfoViewModel parent = null)
    {
        Key = node.Key;
        Parent = parent;
        FileInfo = node.Item;

        var childrenLoader = new Lazy<IDisposable>(() => 
            node.Children
                .Connect()
                .Transform(e => new FileInfoViewModel(e, this))
                .Bind(out children)
                .DisposeMany()
                .Subscribe());

        var shouldExpand = node.IsRoot
            ? Observable.Return(true)
            : Parent.Value.WhenAnyValue(x => x.Expanded);
        
        shouldExpand
            .Where(isExpanded => isExpanded)
            .Take(1)
            .Subscribe(_ => childrenLoader.Value.DisposeWith(cleanup))
            .DisposeWith(cleanup);
    }

    public void Dispose()
    {
        cleanup.Dispose();
    }
}

public IObservableCache<VirtualFileInfo, string> FileInfos => fileInfoSourceCache.AsObservableCache();

public IObservable<IChangeSet<FileInfoViewModel, string>> FileInfoTree =>
    FileInfos
        .Connect()
        .TransformToTree(fileInfo => Path.GetDirectoryName(fileInfo.VirtualPath),
            Observable.Return<Func<Node<VirtualFileInfo, string>, bool>>(node => node.IsRoot))
        .Transform(node => new FileInfoViewModel(node));