TVirtualDrawTree.RootNodeCount Property

Read or set the number of nodes on the top level.

property RootNodeCount: Cardinal;

Usually setting RootNodeCount is all what is needed to initially fill the tree. When one of the top level nodes is initialized you can set its ivsHasChildren style. This will then cause to ask to initialize the child nodes. Recursively applied, you can use this principle to create tree nodes on demand (e.g. when their parent is expanded).

TVirtualDrawTree Class