not complete example

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In example in the component <App /> there is a reference to its method isNodeCollapsed. The problem is that such method is not defined elsewhere in the <App /> component:

https://github.com/pqx/react-ui-tree/blob/6d48ca6d7a7df86655c9a679bc4be3451e0391e5/example/app.js#L43

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what is more weird, isNodeCollapsed is used only once in the library and it doesn't seem to be actually used:
https://github.com/pqx/react-ui-tree/blob/6d48ca6d7a7df86655c9a679bc4be3451e0391e5/lib/react-ui-tree.js#L31
Maybe I am wrong, but it looks for me like it is some part of old api (I've seen that collapsed property is used instead).