Help! What is this stitch called?

Hi there! Knitting a stocking for my son and trying to have the design match my stocking that an old colleague (no longer in touch) made for me.

Does anyone know how to go about intertwining the red yarn onto the green? I’m thinking it might be some duplicate stitch pattern on top, but I’m a little green to knitting and any guidance/help would be BEYOND appreciated!! Thank you!!