The question is what is time complexity?

```
public class Solution {
public TreeNode sortedListToBST(ListNode head) {
if(head==null) return null;
if(head.next==null) return new TreeNode(head.val);
ListNode slow = head, fast = head.next;
while(fast!=null&&fast.next!=null&&fast.next.next!=null){
fast=fast.next.next;
slow=slow.next;
}
TreeNode root = new TreeNode(slow.next.val);
ListNode second=slow.next.next;
slow.next=null;
root.left = sortedListToBST(head);
root.right = sortedListToBST(second);
return root;
}
}
```