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;
          }
      }