C++: Error In Creating Classes

Question

My assignment is to create a general tree, and I decided to do this using three classes: node (contains character data, a pointer to a list ADT which contains all its children, and a pointer to another node for its own sibling nodes), list (contains all the children of a node), and the tree itself. The list is a singly linked list of nodes. The node class is supposed to be used in both the list and tree ADTs. Whenever I try to test my code in main() and see whether the classes are being created properly, I keep getting the error message "error: unknown type name 'list'". Can anyone look at my code and help me figure out how to correctly set up my classes?

//Genghis Khan
#include <iostream>
using namespace std;

class node //will be used for both list and trie ADTs
{
    char character;
    list* child; //all the children of the node will be stored in the list
    node* sibling; //within a list, provides access to all children, functions like a "next"
    friend class list;
    friend class trie;
};
class list
{
private:
    node* head;
    node* tail;
public:
    list()
    {
       head = new node;
        tail = new node;
        head->character = '*'; //head is a sentinel
        tail->character = '*';
        tail->sibling = head;
    }

    void insert(char a) //insertion into the list at the tail
    {
        node* v= new node;
        tail->sibling = v;
        v->character = a;
        v->child = NULL;
        tail = v;
    }

    int size() //so that I can use an empty() boolean
    {
        int size = 0;
        node* temp = head;
        if(temp->character != '*')
        {
            size += 1;
            temp = temp->sibling;
        }
        else
        {
            temp = temp->sibling;
        }
        return size;
    }

    bool empty() //empty condition
    {
        return(size() == 0);
    }

    void print()
    {
        node* temp = head;
        while(temp->character != '*' and temp != tail)
        {
            cout << temp->character;
            temp = temp->sibling;
        }
    }

    friend class trie;
    friend class node;
};
class trie
{
private:
    node* root;
public:
    trie()
    {
        root = new node;
        root->character = '*'; //sentinel
        root->child = NULL; //to be changed when we add children
        root->sibling = NULL; //will never change
    }

    bool haschildren(node* v)
    {
        return(v->child != NULL);
    }


};
int main()
{
    list a;
    a.insert('G');
    a.insert('e');
    a.insert('n');
    a.insert('g');
    a.insert('h');
    a.insert('i');
    a.insert('s');
    a.print();
}

As a note, I tried making "node" a struct instead of a class, but that did not help.