<root>
    <folder name="f1">
        <subfolder>
            <file type="pdf"/>
            <file type="bmp"/>
            <file type="pdf"/>
        </subfolder>
        <subfolder>
            <file type="zip"/>
            <file type="pdf"/>
        </subfolder>
    </folder>
    <folder name="f2">
        <subfolder>
            <file type="zip"/>
            <file type="doc"/>
            <file type="pdf"/>
        </subfolder>
        <subfolder>
            <file type="bmp"/>
            <file type="bmp"/>
        </subfolder>
    </folder>
</root>

f1:
  pdf -  3 
  bmp -  1 
  zip -  1 
f2:
  zip -  1 
  doc -  1 
  pdf -  1 
  bmp -  2 

<xsl:template match="root">
    <xsl:for-each select="folder">
        <xsl:variable name="folderName" select="@name"/>
        <xsl:value-of select="$folderName"/>:<br/>
        <xsl:for-each select="subfolder/file">
            <xsl:if test="not(preceding-sibling::file[@type = current()/@type])">
                <xsl:value-of select="@type"/> - 
                <xsl:value-of select="count(/root/folder[@name = $folderName]/subfolder/file[@type = current()/@type])"/><br/>
            </xsl:if>
        </xsl:for-each>
    </xsl:for-each>
</xsl:template>