I investigate more and I found hidden exception:
{System.InvalidOperationException: Iterating over item that was iterated...
at Telerik.XamarinForms.DataControls.TreeView.TreeViewLayout.PopulateTable
at Telerik.XamarinForms.DataControls.TreeView.TreeViewLayout.PopulateTable
at Telerik.XamarinForms.DataControls.TreeView.TreeViewLayout.PopulateTable
at Telerik.XamarinForms.DataControls.TreeView.TreeViewLayout.AddItem
at Telerik.XamarinForms.DataControls.TreeView.TreeViewLayout.OnCollectionChanged
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged
at System.Collections.ObjectModel.ObservableCollection`1[T].InsertItem
at System.Collections.ObjectModel.Collection`1[T].Add (T item)
at PrismTelerikTest.ViewModels.TelerikTreeViewPageViewModel.OnNavigatingTo