@Override
	public void buildTree() {
		if (scan == null)
			scan = new ScanTask();
		
		//scan has been done previously. "reset" the tree and rebuild from scratch
		else
		{
			root.setChildren(null);
			root.setSize(0); //this will be corrected with the size is recalculated
			totalSize = fileCount = runningTime = 0;
			built = false;
			scan = new ScanTask();
		}
		scan.start();
	}