two-level grouping xslt 2.0

Input:
<book>
<bodymatter>
	<story>
		<cluster_num>Cluster ONE</cluster_num>
		<cluster_head>What Influences a Decision?</cluster_head>
		<thinking_skill>Thinking Skill analyzing</thinking_skill>
	</story>
	<story>
		<pagenum>13</pagenum>
	</story>
	<imggroup>
		<img src="DecisionsDecisions3-web-images/Field%20boy%
20final_fmt.jpeg" alt="missing image file"/>
	<prodnote/></imggroup>
	<story>
		<pagenum>14</pagenum>
	</story>
	<story>
		<story-title>Playing God</story-title>
		<author>Ouida Sebestyen</author>
		<p class="initial-paragraph">He was ...</p>
		<p>So he wasnt going to get away without saying good-bye after
all...</p>
		<!--multiple story, image, and page elements edited out-->

	<story>
		<story-title>TLA</story-title>
		<author>Jane McFann</author>
		<p class="initial-paragraph">I trudged down the hallway of ...</p>
		<p ....</p>
		<!--etc-->

	<story>
		<cluster_num>Cluster TWO</cluster_num>
		<cluster_head>Good Decision or Bad Decision?</cluster_head>
		<thinking_skill>Thinking Skill evaluating</thinking_skill>
	</story>
	<story>
		<pagenum>51</pagenum>
	</story>
	<imggroup>
		<img src="DecisionsDecisions3-web-images/school%20final_fmt.jpeg"
alt="missing image file"/>
	<prodnote/></imggroup>
	<story>
		<pagenum>52</pagenum>
	</story>
	<story>
		<story-title>A Kind of Murder</story-title>
		<author>Hugh Pentecost</author>
		<p class="initial-paragraph">...</p>
</bodymatter>
</book>

I would like to group each <cluster_num> inside <level1> elements and
<story-title> inside <level2> elements

<xsl:template match="bodymatter">
<bodymatter>
<xsl:for-each-group select="*" group-starting-with="story
[child::cluster_num]"> <!--for some reason "story/cluster_num" does
not catch it-->
	<level1 class="unit">
	<xsl:attribute name="unitnum"><xsl:value-of select="position()"/></
xsl:attribute><xsl:text>
		</xsl:text>
	<xsl:for-each-group select="current-group()/*" group-starting-
with="story[child::story-title]">
		<level2 class="selection">
			<xsl:apply-templates select="current-group()"/>
		</level2>
	</xsl:for-each-group>
<xsl:apply-templates select="current-group()"/>
</level1><xsl:text>
</xsl:text>
</xsl:for-each-group>
</bodymatter>
</xsl:template>

<bodymatter>
<level1 class="unit" unitnum="1">
		<level2 class="selection">
<cluster_num>Cluster ONE</cluster_num>
<cluster_head>What Influences a Decision?</cluster_head>
<thinking_skill>Thinking Skill analyzing</thinking_skill>