Varadic and template template parameters and partial specification for tree node class

As the new standard gains popular, programmers are able to use template template parameter along with varadic template to define a class template that looks like:

/* C++ code */
template <template <class...> class container = std::unordered_multimap, typename... args>
class basic_node {
    public:
    container<args...> set;
};

/* class partial specialization */
template <typename key, typename value, typename hash, typename pred, typename alloc>
class basic_node<std::unordered_multimap, key, value, hash, pred, alloc> {
    protected:
    std::unordered_multimap<key, value, hash, pred, alloc> set;
};

My idea is to define a class template that contains a set of its child in the composed container member:

/* We use CRTP to avoid complain about incomplete type tree_node */
class tree_node : public basic_node<
        std::unordered_multimap, 
        std::string, /* key: name tag in text */
        tree_node, /* CRTP on value : element object in container */
        std::hash<tree_node>, /* some compatible hash */
        std::equal_to<tree_node>, /* some compatible equal_to */
        std::allocator<tree_node>> /* some a default allocator */
{
    public:
    /* ERROR: tree_node is of incomplete type because the compiler is now on it */
    //std::unordered_multimap<std::string, tree_node, std::hash<tree_node>, std::equal_to<tree_node>, std::allocator<tree_node>> set; /* inherited members */
};

Is this approach sound? I mean, I used to confuse about the curiously_recurring_template_pattern (CRTP) idiom template tree_node<std::unordered_multimap<tree_node<std::unordered_multimap<tree_node<std::unordered_multimap<...>>>>>>... induced by design but now it seems handy to me if the above works, or maybe?

EDIT:

1. Rectified parameters for std::unordered_multimap.
2. Thanks and CRTP it is by the design.