You focus your Occultist studies on Necromancy, attemping to master the power that controls life and death, to manipulate it to your will. As you progress, you learn to take life from creatures as your power destroys it's body, transforming it's life force into power that you can manipulate as you see fit.
Most see necromancers as menacing abominations, and are believed to be likely part of the Cabal, but not all Necromancers are evil.
When you decide to join the Occult school of Necromancy, you focus your efforts on these texts and their logic is clear to you. The gold and time it takes to copy a necromancy spell into your spell repository is halved.
After joining the Occult School of Necromancy, you quickly learn the ability to grasp hold of the life energy from creatures passing to the Realm of Repose that you killed with your spells.
Once per turn when you kill one or more creatures with a spell of 1st level or higher, you regain hitpoints equal to twice the spell's level, or three time it's level if the spell belongs to the School of Necromancy.
Constructs and the Undead don't pass to the Realm of Repose and so you don't benefit from their deaths from this ability.
You add the animate dead spell to your spell repository if it wasn't already there. \
When you cast animate dead, you can targert one additional corpse or pile of bones, creating another zombie or skeleton, as appropriate.
Whenever you create and undead using a necromancy spell, it has the additional benefits:
Your soul has been touched by necromatic forces for so long, it has grown calluses to their forces.
You have resistance to necrotic damage, and your maximum hitpoints cannot be reduced by any means.
You can attempt to bring undead under your control, even those created by other necromatic wizards. As an action, you can choose one undead that you can see within 60 ft. That creature must make a Charisma saving throw. If it succeeds, you can't attempt to use this feature on it again. If it fails, it becomes friendly to you, and obeys your commands until you use this feature again on another undead.
Undead intelligence varies, and intelligent undead are much harder to control in this way. If the target has an Intelligence of 8 or higher, it has advantage on the saving throw. If it fails the saving throw and has an Intelligence of 12 of higher, it can repeat the saving throw at the end of every hour until it succeeds and frees itself from your influence.