Hi,

I am trying to insert points from a point cloud into an open3d octree. I use this code:

```
# Octree integration test
o3d_pcl_1 = o3d.geometry.PointCloud.create_from_rgbd_image(rgbd1, camera_intrinsics)
o3d_vox_1 = o3d.geometry.VoxelGrid.create_from_point_cloud(o3d_pcl_1, 1e-3)
octree1 = o3d_vox_1.to_octree(8)
o3d_pcl_2 = o3d.geometry.PointCloud.create_from_rgbd_image(rgbd2, camera_intrinsics)
points2 = np.asarray(o3d_pcl_2.points)
for point in points2:
octree1.insert_point(octree1, point)
```

and get this error

```
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-74-0d26b9accd10> in <module>
3 points2 = np.asarray(o3d_pcl_2.points)
4 for point in points2:
----> 5 octree1.insert_point(octree1, point)
TypeError: insert_point(): incompatible function arguments. The following argument types are supported:
1. (self: open3d.open3d_pybind.geometry.Octree, point: numpy.ndarray[float64[3, 1]], f_init: Callable[[], open3d.open3d_pybind.geometry.OctreeLeafNode], f_update: Callable[[open3d.open3d_pybind.geometry.OctreeLeafNode], None]) -> None
Invoked with: geometry::Octree with origin: [-1.32618, -0.938926, 1.0305], size: 2.261, max_depth: 8, geometry::Octree with origin: [-1.32618, -0.938926, 1.0305], size: 2.261, max_depth: 8, array([-1.2268764 , 0.96355541, -0.88814585])
```

What is the problem? Does it come from f_init and f_update?