MN/PE2 flexibility

Hi.  So i have mastered MN/PE1 but am having some trouble with the next progression as i cannot get my legs as high as the ones shown in the video.  They begin to bend the higher i go.  What exercise can i do to increase my flexibility in this area so i can perform full reps? Thanks

There are many threads about this as MN/PE2 has been a sticking point for a number of us - just search the forum for "MNPE2."  But the upshot is this: do the Middle Splits Stretch Series and to the extent your recovery abilities allow, supplement with some compression work, e.g. seated straddle leg lifts.