How to know if it's a 2-node or 3-node in a 2-3 tree?

Question

I have a binary search tree, and I created a struct for the node that represents one element and the child to its left, yet, I cannot figure out the mechanism on how to check if it's a 2 node, with one element and two children or if it's 3 node, with two elements and three children. Would someone please give me a hint ?

This is my template class for the BNode

template<class E>
class BNode
{
    public:
        struct Entry
        {
            E value;
            BNode* left;
        };
        bool IsThree();

    private:
        bool _three;
        Entry _first, _second;
        BNode* _right;
};

template<class E>
bool BNode<E>::IsThree()
{
// 

}