>>26253 (OP)you need light wood color and dark wood color, create a cilynder with width wc, then resize offset off the center by wc+spacing, then repeat until the outermost exists the geometrical volume, now this is assuming you have a trunk, if you cut the trunk vertically you should get lines.
Additionally you will need to create some sort of randomization of the circumference and the cylinder walls therefore each cylinder should have n points on the circumference and m points of cross sections vertically, you shall interpolate using either polynomial interpolation or parametrized bezier curves but in 3D space. this way you should get that level of variation wood has