Yes, but it's not really worth it

For one thing, you'll pay 200xp per casting of awaken undead. Also, zombies won't be very useful in combat once you're thirteenth level.

If you want a pyramid of commanded undead, one good way to accomplish that is to gain control of a shadow, which has this power:

Any humanoid reduced to Strength 0 by a shadow becomes a shadow under the control of its killer within 1d4 rounds.

Note that all of these pyramid plans are sort of irresponsible, because if one of your top-level undead gets destroyed, the rest go free.

Yes, but it's not really worth it

For one thing, you'll pay 200xp per casting of awaken undead. Also, zombies won't be very useful in combat once you're thirteenth level.

If you want a pyramid of commanded undead, one good way to accomplish that is to gain control of a shadow, which has this power:

Any humanoid reduced to Strength 0 by a shadow becomes a shadow under the control of its killer within 1d4 rounds.

Some other types of undead can do this too. Vampires will work, for example, if you have access to creatures that can turn into them.

Note that all of these pyramid plans are sort of irresponsible, because if one of your top-level undead gets destroyed, the rest go free.