How to let an object appear from bottom to top with shader graph?

Hi all,

I just want a very basic effect, let a gameobject appear from bottom to up.

My basic idea is make a white bottom and black top image, which slide from bottom to top as alpha value.

Currently I can use the “position” node with the “split” node to access the y value of each vertex. And I also know, I should use a “time” node to control the position, but I still can not figure out, how to make this effect…

Can you give some suggestions? Which nodes should I use and how to connect them together?