subNodes - How do I make new ones? How do I access the ones that are already there?

[Imaginativeone]

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• I'm submitting a ...
  [ ] bug report
  [ ] feature request
  [ x ] question about the decisions made in the repository

• Do you want to request a feature or report a bug?
  No

• What is the current behavior?
  I'm unable to add a node to the list of nodes.

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via
  https://plnkr.co or similar (you can use this template as a starting point: http://plnkr.co/edit/tpl:AvJOMERrnz94ekVua0u5).

• What is the expected behavior?
  I would like to add a node to the list of nodes.

• What is the motivation / use case for changing the behavior?
  Exploring hierarchical trees in the data model

• Please tell us about your environment:
  MacOS 10.13.6
  Angular 7
  Ionic 4

• Angular version: 2.0.0-beta.X
• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]

Chrome

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, gitter, etc)