Let's begin from the waterbomb base form. Then we shall make some actions with each of four pointed elements given by this base form.

In the first, we shall fold each corner to the middle of square. In the second, we shall open and squash the pockets. Then, we shall remove inside of the model the superfluous material. And, at last, again we shall open and squash the formed pockets.

Now lift the triangles from both sides of the central part, and the model is ready.