C++ Multi Level Linked List Add

Question

Hello everyone I'm trying to implement constructer and sorted add method for this this structure but I can not get the idea of the Multi&doubly linked list. Any idea or help? (You can help me with class system or struct system doesn't matter.)

class MultiLLNode {
public:
    MultiLLNode() {
        next_name = nullptr;
        prev_name = nullptr;
        next_ext = nullptr;
        prev_ext = nullptr;
        next_size = nullptr;
        prev_size = nullptr;
    }

    string infos[3]; // infos[0] = name, infos[1] = extension, infos[2] = size
    MultiLLNode *next_name, *prev_name, *next_ext, *prev_ext, *next_size, *prev_size;
};

///////////////////////////////////////////////////////////////////////////

struct Node
{
    struct Node *prev_n;
    string name;
    struct Node *next_n;

    struct Node *prev_e;
    string extension;
    struct Node *next_e;

    struct Node *prev_s;
    string size;
    struct Node *next_s;
}*first=nullptr;

void create(const vector<vector<string>>& A, int n)
{
    struct Node *t, *last;
    int i;

    first = (struct Node *)malloc(sizeof(struct Node));
    first->name = A[0][0];
    first->prev_n = first->next_n = nullptr;
    last = first;
}