How to improve/refactor this xslt? - xslt

Question

Given the following xml :
<tree>
<val>0</val>
<tree>
<val>1</val>
<tree>
<val>3</val>
</tree>
<tree>
<val>4</val>
</tree>
</tree>
<tree>
<val>2</val>
<tree>
<val>5</val>
</tree>
<tree>
<val>6</val>
</tree>
</tree>
</tree>
I need to transform it into this xml:
<root>0
<frst>1
<leaf>3</leaf>
<leaf>4</leaf>
</frst>
<second>2
<leaf>5</leaf>
<leaf>6</leaf>
</second>
</root>
This is my attempt that gives the same result, I recently started learning XSLT i'm not sure what other option I have, can this be improved or done in another way ?
Thank you for your help
This is my attempt :
<?xml version='1.0' encoding='utf-8'?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="UTF-8"/>
<xsl:template match="/tree">
<root>
<xsl:apply-templates />
</root>
</xsl:template>
<xsl:template match="val">
<xsl:value-of select="."/>
</xsl:template>
<xsl:template match="tree">
<xsl:choose>
<!-- IF HAS CHILDREN -->
<xsl:when test="child::tree">
<xsl:if test="(count(preceding-sibling::tree)+1) = 1">
<frst>
<xsl:apply-templates/>
</frst>
</xsl:if>
<xsl:if test="(count(preceding-sibling::tree)+1) = 2">
<second>
<xsl:apply-templates/>
</second>
</xsl:if>
</xsl:when>
<!-- ELSE IS A LEAF -->
<xsl:otherwise>
<leaf>
<xsl:apply-templates/>
</leaf>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>
test test

Answer 1

I would think the conditions can be written in match patterns:
<xsl:template match="tree[tree][1]">
<frst>
<xsl:apply-templates/>
</frst>
</xsl:template>
<xsl:template match="tree[tree][2]">
<second>
<xsl:apply-templates/>
</second>
</xsl:template>
<xsl:template match="tree[not(tree)]">
<leaf>
<xsl:apply-templates/>
</leaf>
</xsl:template>
although I guess your current code doesn't process the third/fourth/fifth.. tree children so an additional <xsl:template match="tree[tree][position() > 2]"/> might be necessary.