Compilation output Mismatch?

// Binary Search Tree Implementation

#include <iostream>
#include <tuple>

using namespace std;

struct node
{
    int val;
    node *left = nullptr;
    node *right = nullptr;
};

node* root = new node; 


/* insert function, takes params as (root node, and value ) to be added to the BST */
void insert(node* t, int a)
{
    if(t->val > a)
    {
        if(t -> left == NULL)
        {
            node* leftChild = new node;
            leftChild -> val = a;
            t -> left = leftChild;
        }
        else
        {
            insert(t->left, a);
        }
    }
    else
    {
        if(t->right == NULL)
        {
            node* rightChild = new node;
            rightChild -> val = a;
            t -> right = rightChild;
        }
        else
        {
            insert(t->right, a);;
        }
    }
}

/* If value a is present in tree return pointer to that node and it's parent.
    The pointers are returned as tuple <node,parent> */
tuple<node*, node*> search(node* t, node* parent, int a)
{
    if (t -> val == a)
    {
        //tuple (child, parent);
        return make_tuple(t, nullptr);
    }

    if(t->val > a)
    {
        if(t -> left == nullptr)
            return make_tuple(nullptr, nullptr);
        else
            search(t->left,t, a);
    }
    else
    {
        if(t->right == nullptr)
            return make_tuple(nullptr, nullptr);
        else
            search(t->right,t, a);
    }
}

int main()
{
    //(Make binary tree out of array elements).
    int arr[6]= {10,5,15,3,7,18};
    root -> val = arr[0];
    for(int i=1;i<6;i++)
    {
        insert(root ,arr[i]);
    }
    //add some more element.
    insert(root, 12);
    insert(root, 11);
    insert(root, 13);
    insert(root, 14);   

    //search element in tree.
    node* mynode; node* parent;
    tie(mynode, parent) = search(root, nullptr, 10);
    
    mynode ? cout << "yes" : cout << "no";
    mynode = nullptr;
    tie(mynode, parent) = search(root, nullptr, 22);  //(nullptr,nullptr) outcome from search, mynode here is nullptr which is correct what I should be.
    
    mynode ? cout << "yes" : cout << "no";              // My code should be a nullptr here but it is not.
    /* In the line above, mynode have the value what it was at line 92. Why? */
}