It's a shrub, not a tree. You could propagate using soft twig cuttings (that is, recent growth from this year) and root hormone powder or liquid and keep it moist.

Here is a link that might be useful: Links to propagation tips from cuttings

Thank you for the clarification. Funny, it looked like a shrub a few years ago but now it's as tall as their house, so I just thought it must be a tree. I appreciate your help on how to propagate them and the link as well. I think I will try to do it.

If you can get several lengths about a foot long of old wood they root quite well just shoved into the ground and kept moist.

Hi floral, thanks so much. You've given me some encouragement. I'm going to try it. Thanks again.

eshga, I think you could justifiably call Elder a small tree. If left unpruned Sambucus nigra grows a single trunk, or at least a small number of trunks and can reach 20 feet or so, easily as big as a Rowan. It's one of those in between sort of woody plants. Old Elder trees are common in the British countryside.

I have Black Lace growing in my yard. I trimmed back the shrubs last fall and stuck the woody stems in an empty planter in my backyard because I heard they were easy to propagate. 3 out of the 5 cuttings sprout leaves this spring. I literally did nothing but water the planter in the spring.