I will post the answers from ticket ID 1051689 here, so others can benefit as well:
The default behavior of the Kendo UI TreeList is to send a request for the child items only when a parent row is expanded. You can confirm this by exploring the Network tab in the browser's developers tools (F12) for the mentioned demo, or in the following dojo, based on the same example:
The length of the dataSource's data is 1 in the beginning, and increases after expanding different items.
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