Activate Warren Soultrader by sacrificing Nether Traitor and paying 1 life.
When Nether Traitor dies, Sek'Kuar triggers, creating a 3/1 Graveborn creature token.
When the Graveborn enters the battlefield, Leyline of Vitality triggers, causing you to gain 1 life.
Resolve the Warren Soultrader ability, creating a Treasure token.
Activate the Treasure by tapping and sacrificing it, adding ({B} magic symbol) .
Activate Warren Soultrader by paying 1 life and sacrificing the Graveborn.
When the Graveborn dies, Nether Traitor triggers, causing you to pay ({B} magic symbol) to return Nether Traitor from your graveyard to the battlefield.
When Nether Traitor enters the battlefield, Leyline of Vitality triggers, causing you to gain 1 life.
Resolve the Warren Soultrader ability, creating a Treasure token.