TBaseVirtualTree.RootNode Property

Reference to the internal root node which is the anchor of the entire tree node hierarchy.

property RootNode: PVirtualNode;

For anchoring the tree hierarchy an internal tree node is maintained which is mostly just like any other tree node but has sometimes differently handled. The root node is always expanded and initialized. Its parent member points to the treeview to which the node belongs to and its PreviousSibling and NextSibling members point to the root node itself to make it possible to actually recognize this node.

You should not use the root node to iterate through the tree. It is only publicly accessible because it is the parent of 

all top level nodes and can be used to test a node whether it is a top level node or not.

TBaseVirtualTree Class