ExpressionTreePlot

ExpressionTree[e]
plots the expression tree of e.

plots the expression tree of e with its root placed at position pos.

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

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

An expression tree up to level 2 with its root at the left:

Needs["GraphUtilities`"]

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

Out[2]=

An expression tree up to level 2 with its root at the left:

Out[3]=

When Hold, HoldForm, etc. are used, the expressions inside them are not evaluated:

This gives an expression tree with no vertex labels, except that all subexpressions are shown as tooltips:

This plots a binary tree:

This plots a 5-ary tree:

TreeForm also gives the expression tree, although the orientation of the tree cannot be specified:

can specify root position: