what is GameObject Structure?

i know that GameObject is the base class for all entities in Unity scenes.

but i want to know the structure of it, i.e: how information is stored and where? where are the object nodes and faces, because i want to make some optimization i want to do progressive mesh, so how can i do this in unity

GameObject itself is only a container for components. If you want to do procedurally generated meshes look at the MeshRenderer and Mesh classes.