code: @Override
      public String toStringTree() {
  		if ( children==null || children.isEmpty() ) {
  			return this.toString();
  		}
  		StringBuilder buf = new StringBuilder();
  		if ( !isNil() ) {
  			buf.append("(");
  			buf.append(this.toString());
  			buf.append(' ');
  		}
  		for (int i = 0; children!=null && i < children.size(); i++) {
  			Tree t = (Tree)children.get(i);
  			if ( i>0 ) {
  				buf.append(' ');
  			}
  			buf.append(t.toStringTree());
  		}
  		if ( !isNil() ) {
  			buf.append(")");
  		}
  		return buf.toString();
  	}
docs: Print out a whole tree not just a node