How to create an assistant that calls available attributes as fast as define dialog

Hi,

Currently I am working on an assistant that one of the feature is to show available attributes from database in a window just like the available attribute from Define Dialog.
I was able to call the available attributes from database in my assistant but it is too slow and each time i expand another folder inside, it takes very long time but the available attributes from Define Dialog
outputs very fast.

Are there any codes or tips on how to call the available attributes without taking too long?

Attached are my codes.

Thank you.