Design and implementation of a 2-3 tree with polymorphism

I have to implement a 2-3 tree using a base class of a node and derived class of leaf and an innernode (i.e both "are-a" node).

But I don't understand how to start with the insertion in simple cases. Since we call the methods of node to insert, how is it supposed to know if what we insert needs to be an innernode or a leaf? And how does a node supposed to change itself to a leaf or an innernode?

Any tips/ideas on how to approach this?

Here's the structure, I didn't get very far though.

typedef int TreeKey;

class node {
public:
    virtual ~node() {}

    virtual void insert(TreeKey k, string d);
    virtual void deletenode(TreeKey k);
    virtual void findnode();
    virtual node * findnode(TreeKey key);

protected:
    struct info {
        TreeKey key;
        string data;
    };
    node* parent=nullptr;
};

class leaf : node {
    info i;
public:
    virtual void insert(TreeKey k, string d);


};

class innerNode : node {
    vector<info> inf;
    vector<node*> vect;

public:
    virtual void insert(TreeKey k, string d);


};