Get Three Level Category and Subcategories through Category id in Root file Magento2

Create a File in Root of Magento2

<?php


 use Magento\Framework\App\Bootstrap;
 require __DIR__ . '/app/bootstrap.php';
 $params = $_SERVER;
 $bootstrap = Bootstrap::create(BP, $params);
 $obj = $bootstrap->getObjectManager();
 $state = $obj->get('Magento\Framework\App\State');
 $state->setAreaCode('frontend');


 
 
    /*$params = (array) json_decode(file_get_contents('php://input'), TRUE);
    print_r($params);                            ////////// Get Data From Postman Api/////////

    $catid=$params['caterory'];
    echo "string+++++".$catid;*/
     
    /*echo"<pre>++";
    print_r($_GET['caterory']);*/                      ////  Get Data Through URL////////

    $catid=$_GET['cateroryid'];

    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
     
  
    $subCategory = $objectManager->create('Magento\Catalog\Model\Category')->load($catid);  //Parent Category ID

    $subcategories = $subCategory->getChildrenCategories();
    //exit();




      //Print suncategory Ids
    
    foreach($subcategories as $subcategorie) {
        $catsubid=$subcategorie->getId().'<br>';
       echo "==============>>" .$subcategorie->getName().'<br>';  
        if($subcategorie->hasChildren()) {
        $childCategoryObj = $objectManager->create('Magento\Catalog\Model\Category')->load($subcategorie->getId());
        $childSubcategories = $childCategoryObj->getChildrenCategories();
        foreach($childSubcategories as $childSubcategorie) {
            //echo"*******". $childSubcategorie->getId();
         echo "*******". $childSubcategorie->getName().'<br>';
           
           if($childSubcategorie->hasChildren()) {
        $childCategoryObj1 = $objectManager->create('Magento\Catalog\Model\Category')->load($childSubcategorie->getId());
        $childSubcategories1 = $childCategoryObj1->getChildrenCategories();
        foreach($childSubcategories1 as $childSubcategorie1) {
         echo"+++++++>>". $childSubcategorie1->getId();
         echo   $childSubcategorie1->getName().'<br>';

           if($childSubcategorie1->hasChildren()) {
        $childCategoryObj2 = $objectManager->create('Magento\Catalog\Model\Category')->load($childSubcategorie1->getId());
        $childSubcategories2 = $childCategoryObj2->getChildrenCategories();
        foreach($childSubcategories2 as $childSubcategorie2) {
         //echo"===>>". $childSubcategorie2->getId();
         echo ">>>>>>". $childSubcategorie2->getName().'<br>';

       
            
        }
     }    

            
        }
     }    



        }
     }    
   

}

 ?>