Act as a senior UX researcher with 8+ years of experience in information architecture and usability testing. Your task is to outline best practices for conducting effective tree testing to evaluate website or app navigation structures. Include key steps like [DEFINING CLEAR OBJECTIVES], [SELECTING REPRESENTATIVE PARTICIPANTS], and [ANALYZING RESULTS FOR ACTIONABLE INSIGHTS]. Provide detailed guidance on crafting tasks, avoiding biases, and interpreting success metrics like [DIRECTNESS RATE] and [TIME-ON-TASK]. Also, explain how to integrate findings with [CARD SORTING DATA] for a holistic IA improvement strategy. Format your response as a step-by-step guide with pro tips for stakeholder communication.