Don't do that , just don't.
you'll have regrets a lot of it.
And I'm serious.
A lot of things will deleted,but by the way, if you already done that don't worry, there is a solutions.
Just run this code in your terminal

sudo apt install ubuntu-desktop
And if you want you can run this one too

#ubuntu-18.04.1
sudo apt install $( curl http://releases.ubuntu.com/18.04/ubuntu-18.04.1-desktop-amd64.manifest | sed -e 's#\t.*##g' )