pub fn leaf<NS, TAG, LEAF, ATT, VAL>(
leaf: LEAF
) -> Node<NS, TAG, LEAF, ATT, VAL> where
NS: PartialEq + Clone + Debug,
TAG: PartialEq + Clone + Debug,
LEAF: PartialEq + Clone + Debug,
ATT: PartialEq + Clone + Debug,
VAL: PartialEq + Clone + Debug, Expand description
create a leaf node