Merge lightening strike video frames into one image

[Ofnuts]

You can try puttin all layers (except the bottom one in "lighten only mode"):

   

To improve this, once you have done that:

• Get the image as a layer: Layer > New from visible
  
• Duplicate that, and Color > Desaturate > Desaturate (Luminance)
  
• Start the Curves tool, the idea is to tweak the image so that, the whole sky becomes white, the lighting becomes black, and the trees stay the same 
  
•    
  
• Open the Channels list, right click any of the RGB channels; and Channel to selection
  
• Hide the desaturated layer, selected the first "New from visible", and decrease the brightness and increase the contrast.