Do you mean visualising the tree by citations? All of these help, but papercube has a good following.

http://flowingdata.com/2012/01/01/visualizing-citations-in-r...

http://webapps.stackexchange.com/questions/10058/visualizati...

http://papercube.peterbergstrom.com/

http://www.cs.umd.edu/hcil/ase/