radzen-blazor/RadzenBlazorDemos/Pages/PanelMenuProgrammatic.razor

@using System.ComponentModel;

<RadzenStack AlignItems="AlignItems.Center" class="rz-p-12">
    <RadzenPanelMenu Style="width:300px">
        <ChildContent>
            @foreach (var item in data)
            {
                <RadzenPanelMenuItem Text="@item.Text" @bind-Expanded="@item.Expanded">
                    <ChildContent>
                        @foreach (var subItem in item.Items)
                        {
                            <RadzenPanelMenuItem Text="@subItem.Text"  />
                        }
                    </ChildContent>
                    </RadzenPanelMenuItem>
                }
        </ChildContent>
    </RadzenPanelMenu>
</RadzenStack>
    
@code {

    static List<MenuModel> data = Enumerable.Range(0, 5).Select(i => new MenuModel(() => data)
    {
        Text = $"Menu{i}",
        Expanded = i == 0,
        Items = Enumerable.Range(0, 5).Select(j => new MenuModel(() => data)
        {
            Text = $"SubMenu{i}{j}"
        })
    }).ToList();

    public class MenuModel : INotifyPropertyChanged
    {
        Func<List<MenuModel>> collection;
        public MenuModel(Func<List<MenuModel>> collection)
        {
            this.collection = collection;
        }

        public string Text { get; set; }

        bool _expanded;
        public bool Expanded 
        {
            get
            {
                return _expanded;    
            }
            set
            {
                if (_expanded != value)
                {
                    collection()?.Where(i => i != this).ToList().ForEach(s => s.Expanded = false);

                    _expanded = value;
                    OnPropertyChanged(nameof(Expanded));
                }
            }
        }

        public IEnumerable<MenuModel> Items { get; set; }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null) 
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}