To care for your bonsai tree during winter, protect it from extreme temperatures by keeping it in a sheltered area. Adjust your watering routine as the soil may dry out more slowly. Reduce or stop fertilization and increase humidity to prevent stress on the tree.  Regularly monitor your tree for pests and diseases and treat any issues promptly. Avoid pruning during winter as it can stimulate new growth that is vulnerable to frost damage. Wait until spring to prune when the tree is actively growing.