I want to convert osgb to b3dm.
For examaple, the osgb data have 10 levels: 0 1 2 3 4 5 6 7 8 9
Now, I want to batch several levels together in one tileset.json. Maybe it should be [0 1 2] [3 4 5] [6 7]  
I do not know which method to split this group is better, maybe it depends on geometricerror, or the number of tiles one json should manage, or other factors.
Can you give me any suggestions or the open source code, so I can understand how Cesium deal with this problem.
Thank you for your help.