Issue with adding additional product partition in shopping campaign with API

[Shijo k j]

I am implementing the code to call the adwords api for shopping campaign. I want to use the feature for product partition under the adgroup criterion service.

I created the campaign with shopping type and created the adgroup under the campaign. And then, I tried to run the example code in AddProductPartitionTree.php. It become success and successfully created tree. 

It contain default production partition  created as 'All products', and all units are under this.

Then I tried to use that default product partition as the parent to create new partition under that. But it returns the error as PRODUCT_PARTITION_UNIT_CANNOT_HAVE_CHILDREN.

I can manually add product partition under the default one on adwords UI then it could be changed to SUBDIVISION type.

I'm wondering is there any runnable example for the shopping campaign case.

Thank you!