I'd add an addition table that links your various records in order to produce your tree structure. A portal to that table can then list related idea records.
Something like this might work:
A new table, RelatedIDeas, would have at least two fields: ParentIdeaID, ChildIdeaID
You'd define a relationship between your two tables as:
MainTable::IdeaID = RelatedIdeas::ParentIdeaID (Select "Allow creation of records via this relationship" for RelatedIdeas.)
You can then select the MainTable table occurrence box in the relationship graph and click the button with two plus signs to make a second table occurrence of it. Name it ChildIdeas and link it to RelatedIdeas like this:
ChildIdeas::IdeaID = RelatedIdeas::ChildIdeaID
Now you can place a portal to RelatedIdeas on your main table's layout and add fields, such as the name of the idea from ChildIdeas to your portal. You can reverse the process by creating a layout based on ChildIdeas and put fields from MainTable in your RelatedIdeas portal.
This is not an undertaking I would recommend to a beginner. Perhaps you should start by reading:
If every idea has ONE parent idea, then there's no need for additional tables.