Actually, you can not make such a shape in our 3-dimension world 🙂 You need to be living in a 4-dimension universe to construct $10$ equilateral triangles with only $10$ matchsticks. The 4-dimension object is called tetrahedral pyramid or 5-Cell. You can imagine it as a 3-dimensional tetrahedron with 4 lines drawn between its center and 4 vertices, such as:
