Tree Container Library

I appreciate your TCL. It is very useful in real world applications. It should be pointed out that, a tree (except seq_tree) implies an partial order just like your design of node_compare_type policy. But, currently, this partial order is hidden in the internal of tree rather than exposed in public interface. For explicitly, here may be 2 patterns available: (Take unique_tree as example)
1. std::map-like interface:
unique_tree<>::insert(key_type parentid, key_type id, stored_type obj), Here stored_type is mapped_type.
original: unique_tree<>::insert(stored_type parent, stored_type obj).

2. functor-based interface:
unique_tree <key_type, stored_type, GetKeyFunctor>::insert(key_type parentid, stored_type obj)
{
// Call pattern #1
unique_tree<>::insert(parentid, GetKeyFunctor(obj), obj);
}

key_type GetKeyFunctor(stored_type obj)
{
return obj.GetKey();
}

Summary: Original tree interface binds key_type and store_type too tightly, because key_type is enough. When searching in the tree or pointing out the parent node, possibly, we do not have the entire store_type but only a key_type. Decoupling the key_type and stored_type may improve TCL usage.