test.xsl:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxml="urn:schemas-microsoft-com:xslt">
<xsl:template match="/">
<xsl:for-each select="//a">
<xsl:value-of select="name"/>
<xsl:variable name="path">
<xsl:call-template name="pathNode">
<xsl:with-param name="node" select="/root"/>
<xsl:with-param name="parentid" select="parentid"/>
</xsl:call-template>
</xsl:variable>

<xsl:variable name="pathNode" select="msxml:node-set($path)"/>
<xsl:for-each select="$pathNode//parentid">
<xsl:sort select="@sortid" data-type="number" order="descending"/>
<xsl:value-of select="."/>==>
</xsl:for-each>
<xsl:value-of select="@id"/>
<br/>
</xsl:for-each>
</xsl:template>
<xsl:template name="pathNode">
<xsl:param name="node"/>
<xsl:param name="parentid">0</xsl:param>
<xsl:param name="sortid">0</xsl:param>

<parentid sortid="{$sortid}">
<xsl:choose>
<xsl:when test="$parentid != ''"><xsl:value-of select="$parentid"/></xsl:when>
<xsl:otherwise>0</xsl:otherwise>
</xsl:choose>

</parentid>

<xsl:if test="number($parentid) >0">
<xsl:call-template name="pathNode">
<xsl:with-param name="node" select="$node/a[@id > number($parentid)]"/>
<xsl:with-param name="parentid" select="$node/a[@id = $parentid ]/parentid"/>
<xsl:with-param name="sortid" select="number($sortid) + 1"/>
</xsl:call-template>
</xsl:if>

</xsl:template>
</xsl:stylesheet>