Check if Tree is symmetrical

SymmetricTree.java

public class SymmetricTree{
 
   public boolean isSymmetric(TreeNode root) {
      
      return isSymmetric(root, root);
  }
 
   private boolean isSymmetric(TreeNode p, TreeNode q){
      
      if(p == null && q == null) return true;
      
      if(p == null || q == null) return false;
      
      if(p.val != q.val) return false;
      
      return isSymmetric(p.right, q.left) && isSymmetric(p.left, q.right);
  }
  
}