Boy are these topics good. I'll try to describe my take on this without being overly messy or complicated.
Objective reality in a nutshell: we are surrounded by an atmosphere, which we call sky. We experience the laws of gravity. We breathe. We wake up every day. Those are parameters that cannot be changed. We are in a human body. Everyone can feel that and integrate this as "objective reality", because everyone experiences it and can attest to experience it.
Where the whole thing complicates is when we start speaking of subjective reality, because there are so many variables that may or may not overlap with objective reality.
Take your example of the tree that falls all alone in the woods. This tree did exist, but we did not perceive it. It fell and made a sound as it fell, but no one heard it. You have two types of people in this case: I'll use the expression of "those who see trees", vs "those who see a forest". The ones who only see trees will say "it did not make a sound, for we would have heard it", but the ones who see a forest will say "it did make a sound, but we didn't perceive it". Those who only see trees concentrate on the immediate aspects of reality and are attuned to the physical first and foremost: the ones who see the forest, however, are more attuned to the big picture and see beyond physical reality.
Take a person who is colourblind. Objective reality says: the sky is blue, the first light in the traffic lights is red, the second orange, the third green. But this person, let's say, is a deuteranope. Deuteranopia causes the affected person to be green-blind: our human will see the sky as blue, yes, but he will see the traffic lights as shades of yellow (if I'm not saying bullshit, I'm not a doc). Another may even be entirely colourblind and sees the world in shades of grey. Yet is their perception unreal? To them it's reality. The fact that they are colourblind does not mean they can't trust their perception: it's simply different.
Take a schizophrenic hallucinating. His hallucinations are very real to him, although they are not to others. Another parameter enters the picture: the unseen. For a world focused on the physical and only the physical, perceiving more is a sign of mental illness, but in societies where the spiritual and unseen is celebrated, such people are considered gods or shamans. His subjective reality has these hallucinations. That doesn't make them less real than objective reality, simply different.
And now the part where my post will probably end up messy as fuck: we feel a lot of things we cannot see, yet we know they are real. From the presence of somebody in a room where there is no one, to simply the air moving around us, those things are very real, yet intangible. That brings us back to the tree example: the sound was simply not perceived, but that doesn't mean it didn't sound. We all know that it sounded, but we cannot prove it, either. I think science may never be able to prove the existence of the intangible: it may just be something that is above human comprehension, or that we aren't supposed to understand until we die. When a relative's mother died and we went to church for her funeral, I could feel her standing in the aisle, yet she was already dead. It however felt just like she was still alive. Was she there? That's possible. In my subjective reality, despite not being seen, she was indeed there. I felt it so strongly I even turned, only to see that, well, obviously, she wasn't standing there. How do people believe in their God without having him in front of them? Subjective reality. This is also why creativity and "madness" are so close to each other and often overlap: the creative person is probably more sensitive to the unseen than others, who cannot share his experience, and thus deem him mad.
Dreams and imaginations are a way to access the unseen. Some dreams (and daydreams) are so vivid you can remember them like physical memories. When you come across someone in a dream, you cannot invent their vibe, especially if you physically never met them. It's especially apparent when you touch them or interact with them. It feels more "real" than the physical reality we live in. Anything that was invented sprung from imagination first: it crossed over into physical reality thanks to the person who decided to create it. It was made "real", but was already real in the first place... ok, I'm starting to get lost in my own reasoning. It's extremely complicated to explain, especially for me, as a very intuitive type of person. I've always known things without being able to put into words. I think this is something you have to experience yourself in order to understand.
Okay, I tried, but this became messier and messier as I went