How to generate multiple YAML anchors and references in Python?

I want to programmatically generate a yaml file using Python that looks as follows(This is a part of the yaml file, the values of the nested blocks, like the count of it, key:value, etc would be coming as an input. FYI).

main_: &MAIN
 key: value
nested_1: &nested1
 <<: *MAIN
 key: value
nested_2: &nested2
 <<: *MAIN
 key: value  

I have tried using ruamel.yaml.comments.CommentedMap and some of its methods like yaml_set_anchor and add_yaml_merge. Here is the code that I have written:

data['main_'] = main_ =  cm(key=value)
main_.yaml_set_anchor('MAIN')
for n in nested:
  # Here n would be 'nested_1','nested_2', and so on..
  data[n] = nested_ = cm(key=value)
  nested_.yaml_set_anchor(n)
  nested_.add_yaml_merge([(0,main_)])

When this gets executed, what I get in the output is this:

main_: &MAIN
 key: value
nested_1:       ---> Anchor Missing Here
 <<: *MAIN
 key: value
nested_2:       ---> Anchor Missing Here
 <<: *MAIN
 key: value 

The line in code does not have any effect. This is probably because the second anchor is not yet merged.

nested_.yaml_set_anchor(n)

So, I try something like this:

for n in nested:
  # Here n would be 'nested_1','nested_2', and so on..
  data[n] = nested_ = cm(key=value)
  nested_.yaml_set_anchor(n)
  nested_.add_yaml_merge([(0,main_)])
  nested_.add_yaml_merge([(0,nested_)]).  ---> Merged to self

And I get this in return:

main_: &MAIN
 key: value
nested_1: &nested1
 <<: [*MAIN, *NESTED1]
 key: value
nested_2: &nested2
 <<: [*MAIN, *NESTED2]
 key: value

Both of them get merged. I do not know how to proceed further with these nested anchors/references.