I have been able to easily create a mesh of a regular tetrahedron thanks to this answer:
However, as you can see, it looks like it's sitting on one of its edges, what I was looking for was for it to be orientated like an egyptian pyramid, i.e. sitting on one of its faces:
But as @YiFan cleverly pointed out, a pyramid is a pentahedron ! So my picture showing an egyptian pyramid is in fact wrong.
Back to my tetrahedron, I can correct somehow the orientation manually but it's imprecise, I rotate on X axis by ~35 degrees and on Z axis by 45 degrees.
How can I rotate a regular tetrahedron so it has the same orientation as an egyptian pyramid, so it looks like sitting on the floor ?