Find parent attribute and append to child

I need to transform some xml files and one of the task is to find an attribute in a specified node and append the attribute value for the child node. For example here is the original xml:

<ParentNode attribute="someValue">
    <ChildNode other_att="foo">
       <OtherNode />
    </ChildNode>   
</ParentNode>

And that's the desired output:

<ParentNode attribute="someValue">
    <ChildNode other_att="foo" appended_attribute="someValue">
       <OtherNode />
    </ChildNode>   
</ParentNode>

I'm just getting familiar with xslt. Here is what I tried to do:

<xsl:stylesheet version="1.0" xmlns:xsl="http://ift.tt/tCZ8VR">
    <xsl:template match="@*|node()">
            <xsl:copy>
                <xsl:apply-templates select="@*"/>
                <xsl:apply-templates/>
            </xsl:copy>
        </xsl:template>

        <xsl:template match="ChildNode">
        <xsl:copy>
                <xsl:attribute name="appended_attribute">
                <xsl:value-of select="'someValue'"/>
                </xsl:attribute>
                <xsl:apply-templates select="@*"/>
                <xsl:apply-templates select="node()"/>
            </xsl:copy>
        </xsl:template>
</xsl:stylesheet>

But it just selected the childnode and append the attribute with hardwired value.

Any advice approciated. Thank you!