Prestashop Back Office Categories Error Notice on line 96 in file /classes/helper

Have you ever experienced your prestashop back office is displaying the add subcategories page in an unusual misaligned way and you are unable to add any new categories as a result. The text and objects are misaligned and there are random flags being generated all over the page. I've run a report and it's returning 

"Notice on line 96 in file /classes/helper/HelperForm.php
 [8] Undefined index: tree"


Alredy tried changing the code to an old backup file from when you know it was working but it's exactly the same and so the problem persists ???

So how to fix this error ? Check for AdminCategoriesController.php file that you can found in /override/controllers/admin/ 
If you see that AdminCategoriesController.php file, try to rename it first and check your prestashop back office try to add some new category. If you can successfully add new category, then the problem is that AdminCategoriesController.php file. 
By default AdminCategoriesController.php is not included in original prestashop installation.