How to achieve texture gradient?

[marigolden]

How do I get a similar stippling effect that is on the lighter parts of the blue & white gradient of these trees? I have a different tree that’s colored solid white aside from its brown trunk so it didn’t stand out of the background I wanted to put it on. So this is the sort of effect I want. I fuzzy selected the top of my white tree, picked 2 color swatches, then stretched the gradient tool in a vertical line. So the coloring’s good to go but I just I don’t know how to get a texture effect that’s concentrated at the top and evenly transitions down like this.. How would you go about it?
Attached file + here is link to the same picture. You have to zoom in to really see it because it's subtle.
https://imgur.com/a/1IkMs3X