To do this stitch, you need to know chain stitch and alternating twisted chain stitch. Knowledge of barred chain stitch will be helpful.

This stitch follows a pattern where each chain stitch loop is followed by an alternating twisted chain stitch loop. I will be demonstrating the stitch on a curved stitch line.

alternating_barred_chain_1       alternating_barred_chain_2
Fig 1: Begin by doing a chain stitch loop followed by a twisted chain stitch loop.   Fig 2: Follow it up with another chain stitch.

alternating_barred_chain_3   alternating_barred_chain_4
Fig 3: Now, follow this chain stitch loop with an alternate twisted chain stitch loop. For that, put in the needle on the right side of the chain stitch and loop the thread around the needle as shown.   Fig 4: When you pull out the needle, you will get a pattern of this sort. Continue with this sequence of stitching.

Fig 5: The pattern, once finished, would look like this. Just remember to alternate the twisted chain after each chain stitch. So, you would put in the needle on the left once and on the right the other time.