@Override
    public String toString() {
        if ("".equals(name)) {
            return root.toString();
        } else {
            return name + ": " + root.toString();
        }
    }
Sets the root of the expression tree of this expression.

@param root The root node to set.
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/RankingExpression.java