Changing the tool tip as the mouse pointer moves along different tree control items is fairly simple. The tree control can be on a dialog, property page or a form view.
Assuming that you use a class derived from CFormView called CMyFormView, which has a tree control, the steps to follow are:
Declare a member variable for the tree control (IDC_TREE1), m_tree.
Decide on how the tip for each tree item will be stored. For instance, you could hold the tip in a map which you declare in the header file CMyFormView.h.