Hola fijate que los nodos tienen una propiedad Nodo.Expanded = true
Private Sub Form_Load()
Dim i As Long
Dim j As Long
Dim N As Node
TreeView1.LineStyle = tvwRootLines
For i = 1 To 10
Set N = TreeView1.Nodes.Add(, , , i)
For j = 1 To 5
Call TreeView1.Nodes.Add(N, tvwChild, , j)
Next
N.Expanded = True
Next
End Sub