Hi,
You cannot instantiate an abstract class - you can create an instance of one of the classes that inherit from NTreeLayout - for example NBalloonTreeLayout, NLayeredTreeLayout, NCompactDepthTreeLayout, NTipOverTreeLayout etc. The following example shows the different types of layouts:
VB.NET Examples \ Layouts
take a look at Compact Depth Tree Layout, Layered Tree Layout and Tip Over Tree layout.
Let us know if you meet any problems or have any questions.
Best Regards,
Nevron Support Team