Korach took himself
What he took is not stated.
Some versions say, “Korach took men”.
The Targum Onkelos says, “Korach separated himself” – he betook himself to the other side of the situation and mounted a mutiny against Moses.
The Talmud (Sanh. 109b) says he took upon himself a bad deal, getting saddled with a rebellion which he had no chance of winning.
The d’rash, the homiletical view, also deserves to be mentioned, that what was wrong with Korach was his character. He was a taker and not a giver.
He wanted everything for himself, without a thought to what he could contribute to the wellbeing of the community.