Science is nothing but interpretations of observations ... interpretations which make testable, predictive claims that can thus be corroborated or falsified with additional observation and/or experimentation.
The nested, hierarchical tree of life is concrete evidence of evolution -- it's almost literally concrete -- it's there in the rocks, in the DNA, in the natural world. If you want to preserve your intellectually honesty, you can't simply reject the tree of life as a "picture," because it's a picture that's been constructed from the meticulous collection of thousands of pieces of evidence. That's what scientific models and theories are ... collections of facts, evidence, natural laws and explanations, woven together into a consistent "picture" that gives us a broader understanding of the world that allows us to make successful predictions as to what will occur.
If you want something you can hold in your hands, go to a local natural history museum and look at the hominid fossils, or those of any past species, and observe the clear progression that has occurred over the eons. Or look at the chickens with tooth buds, the dolphins and whales with leg buds, the human beings with tails. These are vestigial features that linger in the DNA code of living organisms that are sometimes reactivated (not recreated) by a mutation or a scientist's genetic intervention ... and not coincidentally, the vestigial features that manifest themselves in this respect are ONLY the ones that are predicted by modern theories of common descent (that is, humans have the genes for growing a tail, but don't have the genes for growing feathers -- because we evolved from creatures with tails, not creatures with feathers).
If you deny this evidence and deny evolution's validity, then you might as well deny anything a scientist ever tells you, because the standard of proof you're requiring models and theories to live up to precludes the acceptance of any theory that is not blatantly and obviously true without any additional study or abstraction (and the reason we have science is to uncover truth that ISN'T obvious or may in fact contradict fallible human intuition). If you want to reject nearly all of modern science, from biology to geology to physics to astronomy to cosmology ... that's your prerogative.
Edit: Microevolution and macroevolution have both been observed. When scientists use the term "macroevolution," what they're really talking about is speciation, which is the transformation of a population of organisms that makes it so they can no longer breed with the population they arose from. People often misunderstand macroevolution to mean "large scale morphological change," but macroevolution can often result from very tiny changes (much less visually dramatic than some cases of microevolution). In any event, there is nothing to prevent small-scale changes from eventually producing the sort of large scale morphological change that creationists demand (over a sufficiently large number of generations), and the aforementioned evidence overwhelmingly suggests that such a compounding of small changes is exactly what occurred ... yes, going back to our earliest ancestor.
Of course there isn't concrete evidence that confirms every segment of every step of the process (you have to admit that it would be ridiculous to demand a complete fossil of for every individual organism in our ancestral lineage, even though each individual contributed slightly to where we ended up) ... but there is a lot of evidence and the pattern is quite clear. As I said, though, if you don't want to believe it, that's your decision and nobody can force you to change your mind.