Bleach Bypass in Kdenlive

Hello guys

Anyone knows how to do bleach bypass in KdenLive?

Duplicate the video strip, desaturate the top strip to B&W, maybe adjust it's contrast for more severe look, blend between the B&W and color original to get the effect you're happy with?

Great. Could You help me and write a step-by-step instructions? I came here from A.Premiere and benn using Kdenlive for just a few days :(

And Bleach Bypass is very cool effect - more Kdenlive users would benefit from your instructions:)

Ok - last thing I don't understand - how to blend two videos - one with effects, one without.