You just need to enable viewing types through menu File → Options… → Browser and checking Types:
According to pgAdmin’s documentation:
The list of check boxes is used to select which object types to show
in the browser tree. By default, only the most commonly used object
types are shown. Reducing the number of object types shown can
increase the speed of pgAdmin when querying the system catalogs. Use
the Default button to reset the list to its default settings.