At mx:Tree the folders has a folder icon and a disclosure icon(grey arrow in default style). I can easily set different folder icons with iconFunction. How can I change the disclosure icons? (I want to set different icon to each folders).
You can set this using the disclosureClosedIcon and disclosureOpenIcon styles. You can specify a TreeDisclosureClosed and a TreeDisclosureOpen symbol in an assets.swf (Flex 3 skin style).
See the mx:Tree documentation for further details.