double treble Y stitch ~ dtr-Y

Yarn over hook twice, insert hook into next stitch, yarn over and draw up a loop. (4 loops on hook).

Yarn over hook and draw through 2 loops, yarn over hook and draw through another 2 loops, yarn over hook and draw through the remaining 2 loops.  (1 loop remains on hook).

ch2,  then push the hook through the double treble stitch you’ve just made just above the bottom wrap (marked blue on the picture above),

yarn over and pull through loop (3 loops on hook), yarn over and pull through all 3 loops on hook. (1 loop on hook) .