public void insert (double item) {  



    first = insertH (first, item);

  }
  private static Node insertH (Node x, double item) { 
    if (x == null || x.item >= item) {
      return new Node (item, x);
    } else {
      x.next = insertH (x.next, item);
      return x;
    }
  }

Easiest to write, once you understand it.

Some common mistakes:

• Forget to update first in the starter.
• Forget to update x.next in the helper.
• Forget to return x in the helper.