Is it possible to merge a mesh and point cloud into a single model?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

I want to merge a mesh and point cloud into a single model (.ply) and apply LOD (level of detail concept) so that at particular camera position mesh is displayed and at another camera position point cloud is displayed in the viewer.

I read the below documentation, but it does not merge two models into a single model.
http://www.open3d.org/docs/latest/python_example/geometry/point_cloud/index.html#point-cloud-transformation-py

Is there any available code that performs the above operation? please let me know.

Thanks in advance.