Out of curiosity I have been researching the topic of Voxels Engines and I discovered this project Umbra Voxel Engine.
The author does not provide the source code, but can be achieved using ILSpy, I've got.
It is an excellent starting point for building your own Voxel Engine.
Appears some errors in the code:
new Octree(size / 2, data, absoluteBlockIndex + ...
you just have to modify it by the following code:
new Octree((byte)(size / 2), data, absoluteBlockIndex + ...