How to flatten tree via LINQ?

Question

So I have simple tree:

class MyNode
{
 public MyNode Parent;
 public IEnumerable Elements;
 int group = 1;
}

I have a I

Answer 1

A really other option is to have a proper OO design.

e.g. ask the MyNode to return all flatten.

Like this:

class MyNode
{
    public MyNode Parent;
    public IEnumerable Elements;
    int group = 1;

    public IEnumerable GetAllNodes()
    {
        if (Elements == null)
        {
            return Enumerable.Empty(); 
        }

        return Elements.SelectMany(e => e.GetAllNodes());
    }
}

Now you could ask the top level MyNode to get all the nodes.

var flatten = topNode.GetAllNodes();

If you can't edit the class, then this isn't an option. But otherwise, I think this is could be preferred of a separate (recursive) LINQ method.

This is using LINQ, So I think this answer is applicable here ;)