Docker Content Trust / Notary - single root key

I was trying to initialize two repositories following the concept from this documentation, with same root key

The command does accept my root key password, and then it generated all the remaining keys timestamp, snapshot, and repository keys, etc.,
When did an inspect , it is showing new root key, not the one i passed.

Am i missing some steps to achieve this or is it even possible to use same root key for two collections as in the documentation, i appreciate any
inputs on this.