Start with new document, fill background with solid green color.

Apply the following layer effect - Gradient overlay, 150%, white-to-black, radial, blend mode = color burn, effect opacity = about 25-30%

Set foreground color to very dark green (almost black but not entirely), select Pen tool, and start drawing very thin curve...

...looking like this.

Resize the curve (Ctrl-T) so that it take a bit more than half of image.

Duplicate this vector many times similar to shown here. There are several ways to do so. One way is to select path with Path Selection Tool (A) and hit Down arrow while holding Shift and Alt keys.

When ready, duplicate this set of shapes and flip them horizontally.