How do I make my hair so smooth it looks like glass?

…when my hair is in the bun. I put my hair in the bun for my dance competitions. I want it to look very smooth and shiny. How do I do that? If I just use hair gel it is pretty smooth but not as shiny and smooth as some other people have it. Some people make it so smooth it looks like glass surface. Is there a trick or special hair poduct that helps to achieve that? I have long straight hair.