Compound of tetrahedra

A compound of tetrahedra might be:
 * Compound of two tetrahedra – stellated octahedron
 * Compound of three tetrahedra
 * Compound of four tetrahedra
 * Compound of five tetrahedra
 * Compound of six tetrahedra
 * Compound of six tetrahedra with rotational freedom
 * Compound of ten tetrahedra
 * Compound of twelve tetrahedra with rotational freedom