Convert Sorted List to Binary Search Tree java

public TreeNode sortedListToBST(ListNode head) {
         if(head==null) return new TreeNode(0);
            ArrayList<TreeNode> arr=new  ArrayList<TreeNode>();
            while(head!=null)
            {
                arr.add(new TreeNode(head.val));
                head=head.next;
            }
            
           return  BST(arr,0,arr.size()-1);
        }
     TreeNode BST(ArrayList<TreeNode> list,int start,int end)
     {
         if(start>=end)
         {
             return list.get(start);
         }
         else
         {
             int mid=start+(end-start)/2;
             TreeNode root=list.get(mid);
             root.left=BST(list,start,mid-1);
             root.right=BST(list,mid+1,end);
             
             return root;
         }
     }