if using max.... it's the first shape mirrored and then rotated 120 degrees twice the geometry is edit mesh on top of a spline shape which was created using edit spline booleans you need to then manually refine the spline to get the required geometry density then it's just mirror clone rotate the base splines... as you can see I could have been a bit more consistent with the refine, it's worth noting that you should be really sure that you have a copy of the shape before refinement as it's a bugger to edit after.
The USD Team at Autodesk has just open-sourced the 3ds Max USD Plugin on Github. We look forward to those starting their USD adventure to share feedback and help participate in the future of the plugin in Max. We hope you enjoy!