Forms :: Tree Node Icons And Where Icon Files Are Located?

Tree node icons. I created a table named TEMP_USER_MENU and contains the following structure

USER_IDVARCHAR2(15)N
MENU_IDNUMBER(15)N
MENU_DESCVARCHAR2(150)N
FILE_NAMEVARCHAR2(100)N

[code]...

Now all i wanted is to change each node icon. This query just make the parent nodes icon to OPEN folder like icon and the leaf node to FILE. You can see the decode query up there. It just chose the icons from the File_Name field when it founds 0 then it shows it's a parent node it makes it icon to OPEN else it make it to NEW.

Fist thing i want to know that from where the form builder is fetching these icons? i.e. from which path and what format it looks like a .png file ? .ico or a .jpeg file. I have searched a lot online but all in vain.

Second thing if i want to add unique icons in my menu tree on each node. Is there any possibility ? if yes. Then where should i keep my icons files and in which format?