Gradient’s parameters. 
Copy the new created layer 31 times. Minimize then five of the copied layers, applying
Free Transform option. Place them like the next picture shows it.

Merge now all 5 first copied layers in a group. Copy then the new created group and apply free Transform option again to turn it around on 180 degrees, like it is done in the next image.

Change the gradient’s direction on the layers from new made group to look exactly like next picture.
The rest of the copied layers must be changed also, using
Free Transform option. Place them the same way it is done below.

Take the instrument

and represent the tree’s lights, composed of white circles of the same sizes, like in the next picture.

Having the same instrument

, represent now a fir – tree’s ball (circle) with the indicated parameters.

Fill 0% on the layers.
Blending Options-Gradient Overlay
Gradient’s parameters. 
Copy the recently created layer 3 times and apply
Free Transform again where it is necessary. Maximize, minimize and place everything out like it is demonstrated next step.

Take the following instrument

and make one more fir-tree ball with the shown parameters.

Fill 0% on the layers.
Blending Options-Gradient Overlay
Gradient’s parameters. 
Copy the new made layer 6 times and apply
Free Transform selection again where it is necessary to minimize or maximize the picture. Place then everything out like it is demonstrated next picture.