Tree Data Structure OOP Design Problem (C#)

I have a tree structure design problem, and i can't think of a way out.

i want to have one class Tree containing a generic data, and extend the Tree class with ComplexTree that will contain more methods like Iterate, DoSomthingOnComplex, etc.

here is a sample of the code i have:

class Tree<TData>
{
    public TData Data { get; set; }
    public ICollection<Tree<TData>> Children { get; private set; }

    public Tree<Data>(TData data)
    {
         // ...
    }

    public void Iterate(Action<TData> action)
    {
         action(Data);  
         Children.ForEach(x => x.Iterate(action));
    }
}

class ComplexTree<TData> : Tree<TData>
{
    public int ComplexValue1 { get; set; }
    public int ComplexValue2 { get; set; }

    public ComplexTree(TData data, int cv1, int cv2)
        : base(data)
    {
         // ...
    }

    public void DoComplexStuffOnTree()
    {
         // ... might want to use the base methods here
    }
}

problem is that for one thing, i can't really expose the collection that holds Tree to anyone that has create ComplexTree and i can't use Iterate for the ComplexTree because i can't use the cv1, cv2 values that belong only to the inheriting tree.

is there an obvious solution i'm missing? should i not use inheritance? should rewrite all the methods?

Thanks, John