This paper addresses the problem of kinodynamic motion planning, which involves calculating collision-free trajectories while respecting a robot's dynamic constraints. Existing sampling-based planners (SBPs) suffer from slow exploration speeds due to random action sampling, while learning-based planners suffer from poor generalization performance and difficulty in ensuring safety. In this paper, we present the "Diffusion Tree (DiTree)" framework, which efficiently guides state-space exploration of SBPs by utilizing diffusion policies (DPs). DiTree combines a DP action sampler trained in a single environment with an RRT planner, providing a safe and efficient solution for complex dynamic systems. Experimental results show that DiTree is three times faster than existing SBPs and improves the success rate by approximately 30%.