KAṬHA UPANISHAD · 2.3.1

ऊर्ध्वमूलोऽवाक्शाख एषोऽश्वत्थः सनातनः ।
तदेव शुक्रं तद्ब्रह्म तदेवामृतमुच्यते ।
तस्मिँल्लोकाः श्रिताः सर्वे तदु नात्येति कश्चन । एतद्वै तत् ॥ १॥

ūrdhvamūlo’vākśākha eṣo’śvatthaḥ sanātanaḥ ।
tadeva śukraṃ tadbrahma tadevāmṛtamucyate ।
tasmim̐llokāḥ śritāḥ sarve tadu nātyeti kaścana । etadvai tat ॥ 1॥

This is the eternal uswattha tree whose roots are aloft, but its branches are downward. It is He that is called the Bright One and Brahman and Immortality, and in Him are all the worlds established; none goeth beyond Him. This is the thing thou seekest.

Sri Aurobindo · CWSA 18, p. 123