There is a strong electrical potential between the Earth ground and the ionosphere, and it increases by about 100 volt every meter. By attaching a wire into the ground, and lifting it up 120 meters, the guy in this video can drive a very low-current motor. There is no mystery about that. The guy in the video says the effect works by positive charges in the sky absorbing the negative electrons from the ground that can pass through the wire. These charges are of course hydrogen ions, and, they neutralize the electrons in the cathode reaction 4 H+ + 4 e- + O2 --> 2 H2O, producing water. This reaction allows the electrons to continuously flow up the wire (just a few miliamps at most according to the guy in the video), it requires O2 and H+, and it produces water.
So now you can see how raising a conductor into the air, will generate water using the electrical potential difference between the top of the conductor and the ground. Trees, clearly, rise up into the air for whatever reasons. They also, clearly, send roots into the ground, for whatever reason. You can now see how a tree, if it were conductive to electrons, would be able to generate "rain" in the air above it, whilst also being able to extract the electrical current that does that for useful work.
This is also what "lightning" is, there is a buildup of electrical potential, and the electrons from the ground pass upwards to neutralize the H+, and produce water, as in, clouds.