C# treeview or datagrid view indenture parent child list

1. Load tree view with, child relationship in tree view.

  Question: Do I preload the data then ping the preloaded list when user ask for information, or ping the database
                  when user ask for information.

    Question. Upon setting the datasource how to show all the parent, and child, education in the tree view. Do I
  have to call getdata() or fill on all three tables, Can you point me in the right direction.

Can you send me example