We are trying to show the tree structure in the combo box using the following source https://fiddle.sencha.com/#fiddle/g50&view/editor
We are able to view the tree structure in the combo box however when we select any node its not being displayed in the combo box.
There is a treepicker component available in ExtJS 4 and ExtJS 6. From the fiddle you have provided, I can see that you use ExtJS version 5, but I could not find any reference to the treepicker in the API Docs for this version. You can sneak peek into the version 4 and 6 implementation.
But basically, you just missed setting an event listener on the tree panel picker that will update the value of the field: https://fiddle.sencha.com/#fiddle/2qt0&view/editor
