Perhaps this anecdote will relate, or perhaps not. A few weeks ago I was trying to explain to a co-worker why I don't think time "exists". His response was that a second is based, objectively, on the amount of time a certain molecule takes to decay; I found it very hard to find the language to explain to him why that was still subjective, but I'll lay it out here. Holding off on the question of whether a person can actually "experience" what he described, even a calculated observation is a subjective experience.
Taking time as the question, we've probably all experienced an hour that lasts an eternity or a day that lasts about a second. The "objective" answer to this issue might be that there wasn't a stable measurement available, we didn't have a clock, or an even more accurate measure. The issue for this is that measurement is still interpretation. Even if we could see the decay of molecules, actually see the pattern of decay, the fact that we give this process a name and a meaning is subjective, it has to do with the way a mind might work. It has to do with value all the way down, with a want to determine that there is something we experience called time, that someone wants to measure it, that this measure has any meaning/relates to something "real".
To talk about things that are perhaps more "concrete" like the tree/whatevs, the concepts of existence, of what is alive and how we relate it it/it relates to us are subjective. To say that something truly exists is not only to make a subjective judgement, but to also make a large claim to knowledge that I'm not interested in. To get woo for a sec, I'm more interested in how a tree experiences me and how I experience the tree, and how this is only the surface level of an enormous ball of relationships.
Also, sorry if none of that made any sense.