It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said regarding «كشجرة طيبة» that it is the tree whose leaves do not fall, and I think that it is the date-palm tree.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5647