how can we see the div items using z-Index property

hi.....

here i am using data Table and Tree view and both i made droppable,draggable.once i drag from tree view to Data Table i can able to see the dragged item of tree Node.But when i drag from data Table Onto the tree view ..I am unable to see the dragged column of Data table.here i used z index property for both controls.I done like this:
$(".treeViewReports-Leaf").draggable({
helper: 'clone',
revert: true,
cancel: "treeviewDiv",
start: function () {
$(".treeViewReports-Leaf").css({ 'z-index': '10' }); //with this i can able to see the tree view item on Data Table 1.9
}
}); var colCount = $("#dataTable tr th").length;
for (var index = 0; index < colCount; index++) {
colHeaders = $('#dataTable')[0].rows[0].cells[index];
}
$(colHeaders).draggable({
revert: "invalid",
start: function () {
colName = this.title;
$("#treeViewDiv").css({ 'z-index': '-1 !important' }); //here i am removing z-Index property for tree view div
$("th.ui-draggable").css({ 'z-index': '999999999', 'position': 'relative', 'display': 'block' });//i given data table columns z index property..but this is not applying.. i am unable to see the Data table item on tree view
}
}); //End OF Making All Columns Draggable

please corrupt my code ..and give me guidence

Thanks in advance.....

ManoRama