When you say an infinite number of things exist in the universe, you're recognizing that there are differences between things. Differentiation is a fundamental characteristic of the universe. But individual or type difference does not indicate separation from a common root. For practical purposes, we can believe that all of the different things in the universe are interconnected within a single thing, the one universe. If you use the analogy of a family tree, everything sprang from one creative activity.
Distinctive difference is as important in the universe as it is in our bodies.
If you can carry this awareness of the importance of differentiation and the resultant diversity to other life forms, other physical forms, or other social, ethnic, national, political, and economic forms, then you're on your way to understanding oneness. Thus there is no actual separation between things, only branches of variations on a theme rooted in the universe. There are principals and forces binding together the different components of the universe in ways that we are just beginning to grasp with our sciences and our minds. I'm advocating a perception and an awareness. I'll leave it up to others to prove or disprove what I've come to believe.