Hello Mark, 

Thank you for using our community.  

Let me answer your questions sequentially: 

1. 1.Yes, the igTree support tri-state checkboxes. Here is a link to our online sample that demonstrates how to enable the checkboxes:

   https://www.igniteui.com/tree/drag-and-drop-single-tree

   Link to our API: http://www.igniteui.com/help/api/2016.2/ui.igtree#options:checkboxMode

   Help guide: https://www.igniteui.com/help/igtree-configure-checkboxes-and-selection

2. 2.The Data structure can be any of the following:

Well-formed JSON or XML supplied locally or from a web server 
Nested UL HTML elements 
OData services 
JSONP 
IQueryable in ASP.NET MVC

Link to the help: https://www.igniteui.com/help/igtree-data-binding

Link to sample: https://www.igniteui.com/tree/html-binding and https://www.igniteui.com/tree/xml-binding

API: http://www.igniteui.com/help/api/2016.2/ui.igtree#options:bindings

1. 3.Yes, we support Angular too. Here is a link to the sample: http://igniteui.github.io/igniteui-angular2/samples/igTree/igTree.html and http://igniteui.github.io/igniteui-angular/samples/igTree.html

1. 4.Yes, we support Bootstrap 4. Here is a link to our sample: https://www.igniteui.com/themes/bootstrap4-default

    

I hope those resources will help you create your igTree project. If you have further questions, don’t hesitate to contact us.

Best Regards,
Marina Stoyanova,
Software Developer,
Infragistics, Inc.