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.
Nevron Support Team