How to set up tessellation in GLSL shader?

Question

Unity

I made a GLSL shader for a material with a height map. There was a need to add tessellation, since there is not enough vertex mesh in the vicinity, and I don’t want to generate a model of higher quality, and so on, you even need to reduce it. Distance changes will be quite frequent, so I think tessellation is justified here.
In Unity3D/GLSL shader code is framed by #ifdef ... #endif, tried something like:

#ifdef TESSELLATION

#endif

Zero reaction.
PS For the time being I'll be kosing in HLSL, but I'd like to take a look at GLSL as well.
PSS After surfing the Internet, I got the impression that you can only write vertex and fragment shaders.

Answer 1

Tessellation appeared in OpenGL 4, but as far as I understand, Unity does not support it in the current version. There is a chance they will add it to Unity 5.