TinkerCAD is 3D modeller bought by AutoCAD. You can make 3D object very simply. It provides function of object subtraction by which you can subtract one object from other object to complete a shape. It can also import SVG file. Do you know OKMindmap also export file as SVG format. So, I tried export and import it from TinkerCAD, and do little extra work on that to make more 3D-like. So much fun for this.