// internal override IBinaryTree GetRootNode<TKey, TValue>(IImmutableDictionary<TKey, TValue> dictionary)
// {
// return ((ImmutableTrieDictionary<TKey, TValue>)dictionary).Root;
// }
protected void ContainsValueTestHelper <TKey, TValue>(ImmutableTrieDictionary <TKey, TValue> map, TKey key, TValue value)
{
Assert.False(map.ContainsValue(value));
Assert.True(map.Add(key, value).ContainsValue(value));
}