I want to know the grammatical rule of more in the following context and the meaning of going on. Also, why is the verb used in progressive tense?
"When you look at a tree, you may notice only the branches and leaves. A closer look shows that there is actually a great deal more going on. Trees provide home to ... "
Source: IELTS Essential words
To go on with no object is a phrasal verb meaning "to be in a state that is 'in progress' or not stopped."
When used directly it often carries an implication of continuing despite difficulty.
The project goes on.
Life goes on.
More is a pronoun here, and going on is a post-positive adjectival participial phrase modifying more (qualifying more by telling what kind of more).
More is often used as a comparative modifier (It is more cold in here than the other room) but it can also be used as a standalone pronoun, especially when we don't know exactly what the "more of something" is.
