I believe that most spider dreams are positive. So it is with this dream.
Shortly after the dream begins, you sit under a tree. A lone tree or a tree that somehow stands outs from other trees is a common symbol of the dreamer -- especially the dreamer's psyche or the Self. Healthy plants such as large, healthy trees are almost always good signs in a dream. A tree's growth, health and vigor is a reflection of the psychological and spiritual growth of the dreamer.
However, the tree can also symbolize the spinal chord from its base to the top of head. More specifically, it can represent the Sushumna Nadi.
The interpretation of the trunk as representing the spine seems to go along with the spider climbing up its trunk.
As I wrote, I believe that most spider dreams are positive. When I first started noticing people's spider dreams, I didn't have a clue of their possible meanings. Like many dream interpreters, I figured that they were negative symbols. But, then I noticed that they often appeared in the dreams of the more spiritual types.
I would read possible meanings of dream spiders but they were often negative and their meanings never seemed to be a good fit with the dream. I now believe that most spider dreams have these possible meanings:
1. The dream spider might be a symbol of the grandmother spider, which we see in different myths and stories of Native Americans. In these dreams, she would symbolize the Wise Old Woman archetype. When the spider represents this grandmother, she often appears by coming out of a hole in the ground or by climbing down from a spider's thread.
2. When the spider's web is shown in a dream, the web may represent the pathways of the shaman as he or she travels through the alternate reality.
3. But, probably the common meaning of the dream spider (that I see in dreams) is its association with the nadis. I believe that its meaning has something to do with the spider cleaning the nadis or clearing them of (psychic) debris. This is analogous to the spider cleaning its web. I believe that this is the meaning of the spider in this dream.
In your dream, the spider is walking up the trunk. It doesn't seem to be finding too much debris to cleanup.
The color of the spider shows it association with chakras. The green and yellow are the colors that are usually symbolic of the 4th and 3rd chakras, respectively. The two red spots may have something to do with the Ida and Pingala Nadis that are on either side of the Sushumna Nadi. The two red spots on the spider's head could refer to the 6th or 7th chakra, which are inside the skull. (However, the color red is usually associated with the 1st chakra, which is located near the base of the spine.) The arrangement of these nadis and the seven primary chakras looks something like this.
The man who appeared seems to be some sort of spiritual leader or dream guide/guru. Whoever he is, he certainly seems to be very helpful. He tells you that the dream spider is a good sign. And, as you see, I agree with him.
There is a shift in the dream and you are at work. You are riding in an elevator with an open top. The elevator keeps going up. This also a good sign. Your upward journey in the elevator is symbolic of the upward movement of kundalini (or possibly prana). The elevator has an open top, which probably means that you are going way, way up in the elevator.
Hope this helps.