Implementing an AVL Tree using smart pointers Part 2

I made a similar post on here but I did not get any useful feedback. I thus tried to re-do my code a bit to see if that would lead to any decent results. So far my code compiles but yet does not print anything and I am not sure why.

I have an example in int main() that should give me a tree that looks like:

/* The constructed AVL Tree would be
        9
       /  \
      1    10
    /  \     \
   0    5     11
  /    /  \
 -1   2    6
*/

Here is my code:

#include <algorithm>
#include <iostream>
#include <memory>
#include <utility>
#include <stack>
#include <queue>

struct Node {
    int data;
    int height;
    std::unique_ptr<Node> left = nullptr;
    std::unique_ptr<Node> right = nullptr;

    Node(const int& x, const int& y, std::unique_ptr<Node>&& p = nullptr, std::unique_ptr<Node>&& q = nullptr) :
        data(x),
        height(y),
        left(std::move(p)),
        right(std::move(q)) {}

    Node(const int& data) : data(data) {}

};
std::unique_ptr<Node> root = nullptr;

int height(std::unique_ptr<Node>& root) {
    if (!root) return 0;
    return root->height;
}

void fixHeight(std::unique_ptr<Node>& root) {
    auto h1 = height(root->left);
    auto h2 = height(root->right);
    root->height = (h1 > h2 ? h1 : h2) + 1;
}

void rightRotate(std::unique_ptr<Node>& p) {
    std::unique_ptr<Node> q = std::move(p->left);
    p->left = std::move(q->right);
    q->right = std::move(p);
    fixHeight(p);
    fixHeight(q);
}

void leftRotate(std::unique_ptr<Node>& q) {
    std::unique_ptr<Node> p = std::move(q->left);
    q->right = std::move(p->left);
    p->left = std::move(q);
    fixHeight(q);
    fixHeight(p);
}

int heightDiff(std::unique_ptr<Node>& root) {
    if (!root) return 0;

    return height(root->left) - height(root->right);
}

void balance(std::unique_ptr<Node>& root) {
    fixHeight(root);
    if (heightDiff(root) == 2) {
        if (heightDiff(root->right) < 0)
            rightRotate(root->right);
        leftRotate(root);
    }

    if (heightDiff(root) == -2) {
        if (heightDiff(root->left) > 0)
            leftRotate(root->left);
        rightRotate(root);
    }
}

void insert(std::unique_ptr<Node>& root, const int& theData) {
    if (!root) return;
    if (theData < root->data)
        insert(root->left, theData);
    else
        insert(root->right, theData);
    balance(root);
}

auto findMin(std::unique_ptr<Node>& root) {
    while (root->left != nullptr) root = std::move(root->left);
    return root.get();
}

void deleteNode(std::unique_ptr<Node>& root, const int& theData) {
    // Step 1: Perform regular deletion for BST
    if (!root) return;
    else if (theData < root->data) deleteNode(root->left, theData);
    else if (theData > root->data) deleteNode(root->right, theData);

    else {
        // Case 1: No child
        if (root->left == nullptr && root->right == nullptr) {
            root = nullptr;
        }

        // Case 2: One child
        else if (root->left == nullptr) {
            root = std::move(root->left);
        }

        else if (root->right == nullptr) {
            root = std::move(root->right);
        }

        // Case 3: Two children
        else {
            auto temp = findMin(root->right);
            temp->data = root->data;
            deleteNode(root->right, temp->data);
        }
    }

    if (!root) return;

    // Step 2: Update height of the current node
    root->height = 1 + std::max(height(root->left), height(root->right));

    // Step 3: Get the balalce factor of the this node (to 
    // check whether this node became unbalanced)
    int balance = heightDiff(root);

    // If this node becomes unbalanced, then there are 4 cases

    // Left Left Case
    if (balance > 1 && heightDiff(root->left) >= 0)
        rightRotate(root);

    // Left Right Case
    if (balance > 1 && heightDiff(root->left) < 0) {
        leftRotate(root->left);
        rightRotate(root);
    }

    // Right Right Case
    if (balance < -1 && heightDiff(root->right) <= 0)
        leftRotate(root);

    // Right Left Case
    if (balance < -1 && heightDiff(root->right) > 0) {
        rightRotate(root->right);
        leftRotate(root);
    }
}

void inorderTraversal(std::unique_ptr<Node>& root) {
    if (!root) {
        inorderTraversal(root->left);
        std::cout << root->data << " ";
        inorderTraversal(root->right);
    }
}

void preorderTraversal(std::unique_ptr<Node>& root) {
    if (root != nullptr) {
        std::cout << root->data << " ";
        preorderTraversal(root->left);
        preorderTraversal(root->right);
    }
}

void postorderTraversal(std::unique_ptr<Node>& root) {
    if (root != nullptr) {
        postorderTraversal(root->left);
        postorderTraversal(root->right);
        std::cout << root->data << " ";
    }
}

void DFS(std::unique_ptr<Node>& root) {
    if (!root) return;

    std::stack<Node const *> s;
    s.push(root.get());

    while (!s.empty()) {
        auto p = s.top();
        s.pop();

        if (p->right != nullptr) s.push(p->right.get());
        if (p->left != nullptr) s.push(p->left.get());

        std::cout << p->data << " ";
    }
}

void BFS(std::unique_ptr<Node>& root) {
    if (!root) return;

    std::queue<Node const *> q;
    q.push(root.get());

    while (!q.empty()) {
        auto p = q.front();
        q.pop();

        if (p->left != nullptr) q.push(p->left.get());
        if (p->right != nullptr) q.push(p->right.get());

        std::cout << p->data << " ";
    }
}

bool exists(int d) {
    auto temp = root.get();
    while (temp != nullptr) {
        if (temp->data == d) {
            return true;
        }
        else {
            if (d > temp->data) {
                temp = temp->right.get();
            }
            else {
                temp = temp->left.get();
            }
        }
    }
    return false;
}

int main() {

    //        8
    //      /    \
    //    4       10
    //   / \     /  \
    //  2   6   9    12

    //insert(root, 8);
    //insert(root, 10);
    //insert(root, 4);
    //insert(root, 2);
    //insert(root, 6);
    //insert(root, 12);
    //insert(root, 9);


  /* Constructing tree given in the above figure */
    insert(root, 9);
    insert(root, 5);
    insert(root, 10);
    insert(root, 0);
    insert(root, 6);
    insert(root, 11);
    insert(root, -1);
    insert(root, 1);
    insert(root, 2);

    /* The constructed AVL Tree would be
            9
           /  \
          1    10
        /  \     \
       0    5     11
      /    /  \
     -1   2    6
    */

    printf("Preorder traversal of the constructed AVL "
        "tree is \n");
    preorderTraversal(root);

    //deleteNode(root, 10);

    /* The AVL Tree after deletion of 10
            1
           /  \
          0    9
        /     /  \
       -1    5     11
           /  \
          2    6
    */

    //printf("\nPreorder traversal after deletion of 10 \n");
    //preorderTraversal(root);

    /*inorderTraversal(root);
    std::cout << "\n";

    preorderTraversal(root);
    std::cout << "\n";

    postorderTraversal(root);
    std::cout << "\n";

    DFS(root);
    std::cout << "\n";

    BFS(root);
    std::cout << "\n";

    exists(4) ? std::cout << "Yes" << std::endl : std::cout << "No" << std::endl;*/


    std::cin.get();
}