I designed this hat for my sister who has always talked to squirrels and once upon a time had green hair. The tree cable (modified from Barbara Walker’s Third Treasury of Knitting Patterns) sits on a background of reverse stockinette stitch.
It could be done in any light worsted weight yarn. Pattern includes a chart and written instructions for the tree cables.
To decrease the circumference remove stitches from the end of each round. You’ll have to do some finagling with the crown decreases though.
To decrease the depth skip some rows between rows 1 and 8 of the chart.