I am trying to implement a tree in c++ using class

Question

I just wanted to implement a TreeNode class that works similar to that of a struct node for a tree implementation.

Everything is working fine except for the output that is including 0 at the beginning of the inOrder traversal. Can anyone please explain it to me why is that happening?

Input:

22,1,2,3,5,4,11,20,19,24,21

Output:

0 1 2 3 4 5 11 19 20 21 22 24 

#include <bits/stdc++.h>

using namespace std;

class TreeNode{

    public:

        int data;
        TreeNode* left;
        TreeNode* right;

        TreeNode(){
            left = NULL;
            right = NULL;
        }

        TreeNode(int val){
            data = val;
            left = NULL;
            right = NULL;
        }

};

void insertInorder(TreeNode* cur, int d){

    if(d <= cur->data){
        if(cur->left == NULL)
            cur->left = new TreeNode(d);
        else
            insertInorder(cur->left,d);
    }
    else{
        if(cur->right == NULL)
            cur->right = new TreeNode(d);
        else
            insertInorder(cur->right,d);
    }
}

TreeNode* makeTree(vector<int> v){

    TreeNode* root = NULL;

    for(int start = 0; start <= v.size(); start++){
        if(start == 0){
            root = new TreeNode();
            root->data = v[0];
        }
        insertInorder(root,v[start]);
    }

    return root;
}

void printInorder(TreeNode* node) 
{ 
    if (node == NULL) 
        return; 
  
    /* first recur on left child */
    printInorder(node->left); 
  
    /* then print the data of node */
    cout << node->data << " "; 
  
    /* now recur on right child */
    printInorder(node->right); 
} 

int main(){

    vector<int> x = {22,1,2,3,5,4,11,20,19,24,21};

    TreeNode* r = makeTree(x);

    printInorder(r);


    return 0;

}

Edit:

To the people visiting this questions at a future date. Better practices states that we shouldn't use

#include <bits/stdc++.h>
using namespace std;

Using namespace std can result into future namespace collisions in the code. For reference here. I did the same mistake but I won't be doing this from now on.

Please refer to the link provided by @Jabberwocky here