Whipped chain stitch
This stitch is formed of a line of chain stitch with a thread whipped around it. The whipped thread can be the same as the chain stitch thread, or a contrasting one.
At the end of the chain stitch, make a small straight stitch to anchor the last chain.
Introduce a new thread at the top end of the chain stitch. You could use a contrasting colour for a striking effect.
Whip the new thread by passing the needle under each chain stitch. Make sure not to pierce the fabric.
Structure of stitch
Jennifer Campbell, Ann-Marie Bakewell, Guide to Embroidery Stitches (2004) , p.122