You have created a Tree item in Oracle Apex for a particular page to use it as menu and you want that whenever user clicks a node, it will open a correspondent page. So create a table for tree menu with the following fields:
Example table Treemenu:
Create table treemenu ( program_desc varchar2(50), module_code varchar2(50), program_code varchar2(10), page_no varchar2(10) );
Enter the appropriate data in the above table. You can take the idea by the below-mentioned query.
See Also: Oracle Apex Tree Example
Now enter below query in Oracle Apex query area for the tree item:
select case when connect_by_isleaf = 1 then 0 when level = 1 then 1 else -1 end as status, level, "PROGRAM_DESC" as title, null as icon, "MODULE_CODE" as value, null as tooltip, 'f?p=&APP_ID.:'||"PAGE_NO"||':&APP_SESSION.' as link from "#OWNER#"."TREEMENU" start with "MODULE_CODE" is null connect by prior "PROGRAM_CODE" = "MODULE_CODE"