I am trying to use the AdvTreeComboBox component but am having problems because I cannot find any documentation. There is a sample program but it is too limited in functionality to give me a guide for what I need to do. Is there a user guide for this component? A more extensive example that would show, for example, how to know which node a user double-clicked on? Also, the little arrow at the right indicating that there is a drop down is very small. Users may not notice it. How can I make it bolder?

TAdvTreeComboBox is basically a combobox where in the dropdown there is a treeview instead of a regular list. The treeview is a standard VCL TTreeView component accessible via AdvTreeComboBox.TreeView, so all standard VCL TTreeView document applies to this control in the dropdown.
The node a user double-clicked on should be the selected node and can be retrieved via: AdvTreeComboBox1.Treeview.Selected: TNode
The icon in the dropdown button should match the standard TCombobox dropdown look. This button glyph can be customized via AdvTreeComboBox.Button.Glyph: TBitmap

Thanks. I am working on it now but ran into the problem right away that the type TNode is not defined in AdvTreeView or AdvTreeComboBox. There is a type TTreeNode in Vcl.ComCtrls. Is that what you meant?

It is a standard VCL TTreeView in the drop-down, hence TNode is in VCL.ComCtrls

I am looking at the Vcl.ComCtrls unit now. Shoud be current as it says "Copyright(c) 1995-2023". A search for TNode fails.

Drop a TTreeView on the form, it should cause the unit with TTreeNode to be added to uses list.

Yes, I see TTreeNode but I was trying to find the TNode you mentioned earlier.

I was trying to help from smartphone, it is way after office hours here, so I do no have a RAD Studio in front of me. So sorry for the oversight.

No problem. I appreciate your help. Still early here in Hawaii!