Best implementation for Key Value Pair Data Structure?

So I've been poking around with C# a bit lately, and all the Generic Collections have me a little confused. Say I wanted to represent a data structure where the head of a tree was a key value pair, and then there is one optional list of key value pairs below that (but no more levels than these). Would this be suitable?

public class TokenTree
{
    public TokenTree()
    {
        /* I must admit to not fully understanding this,
         * I got it from msdn. As far as I can tell, IDictionary is an
         * interface, and Dictionary is the default implementation of
         * that interface, right?
         */
        SubPairs = new Dictionary<string, string>();
    }

    public string Key;
    public string Value;
    public IDictionary<string, string> SubPairs;
}

It's only really a simple shunt for passing around data.

There is an actual Data Type called KeyValuePair, use like this

KeyValuePair<string, string> myKeyValuePair = new KeyValuePair<string,string>("defaultkey", "defaultvalue");

One possible thing you could do is use the Dictionary object straight out of the box and then just extend it with your own modifications:

public class TokenTree : Dictionary<string, string>
{
    public IDictionary<string, string> SubPairs;
}

This gives you the advantage of not having to enforce the rules of IDictionary for your Key (e.g., key uniqueness, etc).

And yup you got the concept of the constructor right :)

I think what you might be after (as a literal implementation of your question), is:

public class TokenTree
{
    public TokenTree()
    {
        tree = new Dictionary<string, IDictionary<string,string>>();
    }

    IDictionary<string, IDictionary<string, string>> tree; 
}

You did actually say a "list" of key-values in your question, so you might want to swap the inner IDictionary with a:

IList<KeyValuePair<string, string>>