In a two-way half-duplex system where source nodes are equipped with multiple antennas and a relay with a single antenna, we study the diversity multiplexing tradeoff (DMT) achieved by orthogonal decode-and-forward (ODF), orthogonal amplify-and-forward (OAF), non-orthogonal decode-and-forward (NDF) and non-orthogonal amplify-and-forward (NAF), respectively. Their closed-form DMT are derived with given transmission time of each terminal, and optimized by allocating the transmission time. From these analyses, NDF achieves the best performance in terms of DMT in low spectral efficiency scenarios, while NAF outperforms other protocols in high spectral efficiency scenarios.