Overlapping Ground units

I thought some people might need this info and heres how
Place a unit and hold ctrl and keep pressing z and y and ull get a ton of units in 1 spot

No. That undoes and redoes your action. You still place at most one unit.

You must have a slow machine.

No i have a super fast machine hold ctrl then have one finger over z and one over y and keep on pressing back and forth

EDIT: forgot to mention u have to have gem activated