Start with a chain of 20 stitches.

Make a turning chain of 4 stitches. For this stitch, your turning chain counts as the first stitch of your row.

Skip the next stitch and make a treble crochet into the following stitch.

Work a treble crochet into the stitch that you skipped before. Do this by going behind the stitch you just made, then into that stitch from the front to the back.

Repeat steps 3 and 4 until there is 1 stitch left of the row, then make a normal treble crochet into the last stitch

For the next row, make a turning chain of 4 stitches, this counts as your first stitch of the row again.

Skip the next stitch and make a treble crochet into the following stitch.

Work a treble crochet into the stitch that you skipped before. Do this by going behind the stitch you just made, then into that stitch from the front to the back.

Repeat steps 7 and 8 until there is 1 stitch left of the row, work your final stitch into the top of the turning chain below.

Continue working these 2 rows until your desired length.