C++ - Making BST move onto the next node

Question

I need to make a bank system where each customer that registers onto the bank will have a generated Customer ID that is stored inside BST. I brought all the code needed and it works perfectly until I need it to make a new node to store a new customer ID because all it is doing right now is just replacing the new ID with the old ID inside the same node.

{
private:
    int data;
    BST* left, * right;

public:
    BST()
    {
        data = 0;
        left = right = NULL;
    }

    BST(int value)
    {
        data = value;
        left = right = NULL;
    }

    BST* createNewNode(int value)
    {
        BST* newBST = new BST;
        newBST->data = value;
        newBST->left = NULL;
        newBST->right = NULL;

        return newBST;
    }

    BST* Insert(BST* root, int data)
    {
        if (root == NULL)
        {
            return createNewNode(data);
        }
        if (data < root->data)
        {
            root->left = Insert(root->left, data);
        }
        else if (data > root->data)
        {
            root->right = Insert(root->right, data);
        }
        return root;
    }

    void Inorder(BST* root)
    {
        if (!root) 
        {
            return;
        }
        Inorder(root->left);
        cout << root->data << endl;
        Inorder(root->right);
    }
};

#include <iostream>
#include <string>
#include "BST.h"
using namespace std;

class Customer: public BST
{
private:
    int customerID = 1;
    string customerName;
    string customerAddress;
    string customerMobileNumber;
    string customerEmergencyPerson;
    string customerEmergencyPersonNumber;
    string customerEmail;
    string customerFacebook;
    string customerHomeNumber;

public:
    int getID()
    {
        return customerID;
    }

    string getName()
    {
        return customerName;
    }

    Customer(int x, string y, string z, string p)
    {
        x = customerID;
        y = customerName;
        z = customerAddress;
        p = customerMobileNumber;
    }

    Customer() 
    {

    }

    void createCustomer()
    {
        BST customers, *root = NULL;
        root = customers.Insert(root, 1);
        cout << "If you are new to our bank you need to have an ID before you make bank accounts :)" << endl;
        customerID = customerID + 1;
        cout << "Your Customer ID is " << customerID << endl;
        cout << "Customer's name: ";
        getline(cin >> ws, customerName);
        cout << "Customer's address: ";
        getline(cin >> ws, customerAddress);
        cout << "Customer's mobile number: ";
        getline(cin >> ws, customerMobileNumber);
        cout << "Customer's Emergency Contact: ";
        getline(cin >> ws, customerEmergencyPerson);
        cout << "Customer's Emergency Contact number: ";
        getline(cin >> ws, customerEmergencyPersonNumber);
        cout << "Customer's Email address: ";
        getline(cin >> ws, customerEmail);
        cout << "Customer's Facebook name: ";
        getline(cin >> ws, customerFacebook);
        cout << "Customer's home number: ";
        getline(cin >> ws, customerHomeNumber);
        customers.Insert(root, customerID);
        customers.Inorder(root);
    }
};