ExpressionTreePlot

ExpressionTree[e]
plots the expression tree of e.

ExpressionTreePlot[e, pos]
plots the expression tree of e with its root placed at position pos.

ExpressionTreePlot[e, pos, lev]
plots the expression tree of e up to level lev with its root placed at position pos.

To use ExpressionTreePlot, you first need to load the Graph Utilities Package using Needs["GraphUtilities`"].

Needs["GraphUtilities`"]

An expression tree plot, with tooltips for each vertex giving the subexpression from that vertex down: