When creating an authorisation workflow, you have four options for your rule depending on who submits the request:
Themselves.
Their Manager/Additional Manager.
System Admin.
Other user with edit access rights.
When you create a rule to specify that an employee's holiday request first goes to their manager for approval, and then to the head of the department John Dale, ensure you set up an additional rule for the employee's manager. Otherwise, the request auto-approves instead of going to the manager's manager when the manager inputs the request.
This is a great way to ensure that you have the same end approver on each authorisation workflow. The two rules pictorially look like this: