How can I view tracks from different events and how can I visualize them in X3D or OpenGL?

Hi,

I am trying to display tracks from several events on the same 3D structure.
However, I am facing 2 problems:
1)Everytime I change the entry of the TTree by doing "t->GetEntry(j);" to switch to the next event, all previously drawn tracks disappear. 2)I cannot view the tracks in the X3D or OpenGL viewer. I can only see the solid 3D structure in it.

How can I superpose tracks from different events? And what must I do to view them in X3D or OpenGL?