Trouble creating a Binary Tree class with a nested "TreeNode" class in C++

Question

I'm trying to just create a simple binary tree to store integers. I don't want to just create a struct node outside of my class BinaryTree and then instantiate an object of node* inside the BinaryTree class. I want to embed the node class in the BinaryTree class.

Here is the header file I've written so far for the project:

#ifndef HEADER_H
#define HEADER_H
#include <iostream>
using namespace std;

class BinaryTree {
private:
    class TreeNode {
    public:
        int Data;
        TreeNode* Right;
        TreeNode* Left;
        TreeNode() : Right(nullptr), Left(nullptr) {}
        TreeNode(int data, TreeNode* lnode = nullptr, TreeNode* rnode=nullptr) :
        Data(data), Right(rnode), Left(lnode) {}
    };
    TreeNode* root;
public:
    BinaryTree();
    bool Empty() const;
    bool NewNode(TreeNode* node, const int& new_element);
    bool Insert(TreeNode* node, const int& new_element);    

};
#endif

Here is the .cpp realization of these declarations:

#include <iostream>
using namespace std;

BinaryTree::BinaryTree() : root(nullptr) {

}

bool BinaryTree::Empty() const
{
    return (root == nullptr) ? true : false;
}

bool BinaryTree::NewNode(TreeNode* node, const int& new_element)
{
        TreeNode* new_node;
        new_node = new TreeNode;
        new_node->Data = new_element;
        node = new_node;
        return true;
}

bool BinaryTree::Insert(TreeNode* node, const int& new_element)
{
    if (Empty())
    {
        return NewNode(node, new_element);
    }
    else if (new_element < node->Data) 
    {
        return node->Left = Insert(node->Left, new_element);
    }
    else 
    {
        return node->Right = Insert(node->Right, new_element);
    }
}

The specific errors I'm looking at have to do with the bool BinaryTree::Insert function. I get error notifs on the assignment operator = at these two places:

(1): return node->Left = Insert(node->Left, new_element);

(2): return node->Right = Insert(node->Right, new_element);

The following error message shows up when I investigate:

E0513 a value of type "bool" cannot be assigned to an entity of type "BinaryTree::TreeNode *

I cannot for the life of me figure out how to fix this error or what it's specifically addressing. Other examples of a binary search tree with an embedded class utilize these techniques, and yet I cannot make these assignment operators work. I have also tried to change the return type of the functions, without any success.