Here is my code in java but these is issue in my code can anybody correct it without change my logic, hey coders!!! please show your debugging skill and solve it:::

import org.w3c.dom.Node;

import java.util.*; // BST TREE CLASS class TreeNode{ int data; TreeNode left,right; TreeNode(int data){ this.data=data; this.left=null; this.right=null; } }

//Merge 2 BST public class Main { //insert AT BST method private static TreeNode insertATBST(TreeNode root,int x){ if(root==null){ root=new TreeNode(x); return root; } if(x>root.data){ root.right=insertATBST(root.right,x); } else root.left=insertATBST(root.left,x); return root; } private static TreeNode head=null; private static TreeNode pre=null; private static TreeNode bstToDll(TreeNode root){ if(root==null) return null; //inorder form to use form conversion bstToDll(root.left); if(pre==null) head=root; else{ root.left=pre; pre.right=root; } pre=root; bstToDll(root.right); return head; } private static TreeNode mergeBST(TreeNode root1,TreeNode root2){ TreeNode head=null; TreeNode tail=null; while(root1!=null && root2!=null){ if(root1.data<root2.data){ if(head==null){ head=root1; tail=root1; root1=root1.right; } else{ tail.right=root1; root1.left=tail; tail=root1; root1=root1.right; } } else{ if(head==null){ head=root2; tail=root2; root2=root2.right; } else{ tail.right=root2; root2.left=tail; tail=root2; root1=root1.right; } } } if(root1!=null){ tail.right=root1; root1.left=tail; root1=root1.right; } if(root2!=null){ tail.right=root2; root2.left=tail; root2=root2.right; } return head; } private static int countTreeNodes(TreeNode root){ TreeNode temp=root; int cnt=0; while(temp!=null){ cnt++; temp=temp.right; } return cnt; }

private static TreeNode DllToBst(TreeNode root,int n){
    if(n<=0 || root==null) return null;
    TreeNode left=DllToBst(root,n/2);
    TreeNode newHead=root;
    newHead.left=left;
    root= root.right;
    newHead.right=DllToBst(root,n-n/2-1);
    return  newHead;
}
private static void inOrderTraversal(TreeNode root) {
    if (root == null)
        return;
    inOrderTraversal(root.left);
    System.out.println(root.data);
    inOrderTraversal(root.right);
}
public static void main(String[] args) {
    int[] arr1={1,2,3};
    int[] arr2={4,5,6};
    TreeNode root1=null; // nullify root object
    TreeNode root2=null;
    for (int j : arr1) {
        root1 = insertATBST(root1, j);
    }
    for (int j : arr2) {
        root2 = insertATBST(root2, j);
    }

    root1=bstToDll(root1);
    head=null; pre=null;
    root2=bstToDll(root2);
    TreeNode root=null;
  root=  mergeBST(root1,root2);
    int cnt=countTreeNodes(root);

// while(root!=null) { // System.out.println(root.data); // root=root.right; // } root=DllToBst(root,cnt);

}

}