A tree isn't human because there are enough significant physical differences to justify two different names/taxonomic categories. That should have been obvious to you. I don't think we mean exactly the same things when we say "human."
I think that when you say "human," you mean more than just the species Homo Sapiens, you also include the concepts of mind and soul. I think you believe that humans are special, or fundamentally different from other animals.
I don't believe Homo Sapiens are really that special when compared to other animals. We are not the only creatures that have developed tools or language. We are not the only creatures to feel emotions or pain, or to be "aware" of our surroundings. Insect societies are fundamentally not too far different from ours. Dogs and pigs are more intelligent than human infants. Butterflies see the world in colors we can't even imagine.
Our greatest claim to being superior to other animals is probably our accomplishments in the STEM fields. But, in that we are quickly being overtaken by machines.