Multiple LDAP searches

I am setting up freeradius 2.1.6 and seem to be stuck on how do I go about setting up my ldap module to search multiple basedn if the user is not found in the first? I have four that I need to search in my LDAP tree but cannot figure out the correct way to make it search more than one. I feel like this is probably something simple I'm missing but can't seem to see it atm. Thanks Rob