Macro nebts 

macro_rules! nebts {
    ($h:expr, $( $x:expr ),* $(,)?) => { ... };
    ($h:expr) => { ... };
}

Like the crate::nes! macro, but for Binary Tree Sets.

use nonempty_collections::nebts;

let s = nebts![1, 2, 2, 3,];
assert_eq!(3, s.len().get());