how can i implementing collapsible group with checkbox for tree view in angular

I want to create a Tree View component in Angular with Collapsible and checkbox. I want to develop a completely custom tree view with checkbox and collapsible hence no other plugin or Material design we can use.

Please find my code at -

https://stackblitz.com/edit/angular-7xcthz

Here I am able to render tree View with the checkbox on UI. But want to implement the Collapsible functionality -

1. The collapsible group with chevron icon before each parent node
2. The collapsible chevron icon should show for the parent node when the child element is present else it should be displayed with checkbox only not need to show the chevron icon.
3. Common expand and collapsible functionality needs to implement for entire tree.
4. Chevron icon should not display when there is no child node present.

I appreciate your great help.