Which one is not correct about the $2-3$ tree?

All leaves of the $2-3$ tree are at the same level in the tree, so the tree is always height balanced

Every internal node of the $2-3$ tree has either two children $($if it contains one key$)$ or three children $($if it contains two keys$).$ Hence the name

The $2-3$ tree is a binary tree

A node of the $2-3$ tree contains one or two keys