Unable to get the select All checkbox for the SelectCheckBoxMenu (Primefaces component)

I am trying to use a SelectCheckBoxMenu (Primefaces component) in the form. However, for some reason I am unable to get the select all checkbox in the control. We are adding this control for the first time inside the form. So we do not have any css class that may hamper wit the rendering of the selectAll checkbox for the control. Can you guys help me with this?

screenshot of the control