expand children pages in pagetree for current page. Put this into the textarea of: Confluence Admin -> LOOK AND FEEL -> Custom HTML -> At end of the HEAD

confluence_pagetree_extension.html

<!-- 
Original snippet is from
http://www.communardo.de/home/techblog/2011/05/02/improve-the-confluence-pagetree-macro-functionality/
-->

<script type="text/javascript" >
    AJS.toInit(function ($) {
        //first save the original pagetree function "origHideEmptyChildrenContainer"
        var origHideEmptyChildrenContainer = AJS.pagetree.hideEmptyChildrenContainers;
 
        //define our own one and overwrite the original pagetree function "hideEmptyChildrenContainers"
        //this function is called by the pagetree after children loading      
        AJS.pagetree.hideEmptyChildrenContainers =  function(pagetreeChildrenDiv) {
 
            //search for the child element with the style attribute
            pagetreeChildrenDiv.find('span.plugin_pagetree_children_span').each(function(index, item){
                //click on the plus icon to expand the children of the current page
                // confluence 4.x
                //jQuery(this).parent().parent().find('.plugin_pagetree_childtoggle_container a.icon-plus').trigger('click');
                // confluence 5.x
                var elem = jQuery(item);
                // do not toggle the parent of a childs, if child the current page
                if (elem.parent().next().find('.plugin_pagetree_children_span.plugin_pagetree_current').length === 0) {
                    jQuery(this).parent().parent().find('.plugin_pagetree_childtoggle_container a.plugin_pagetree_childtoggle').trigger('click');
                }
            });
            //call the saved original function...
            origHideEmptyChildrenContainer(pagetreeChildrenDiv);
        };
    });
</script>

I created an updated version that works with Confluence 5.5.6.