protected sealed override ReadOnlyEntityTreeNode <TId, TItem> Create(TItem item, ReadOnlyEntityTreeNode <TId, TItem> parent)
 {
     return(new ReadOnlyEntityTreeNode <TId, TItem>(item, parent));
 }
 private ReadOnlyEntityTreeNode(TItem item, ReadOnlyEntityTreeNode <TId, TItem> parent) : base(item, parent)
 {
 }