I don't think cutting it off will harm it but cannot see how you could make another tree from it. However do you realise quite how big these trees grow? They grow to an enormous size and aren't suitable for the average garden.

mmm i think this is a type of palm tree as if you cut off the smaller trunk 2 more trunks replace it! trust me i once cut my indoor palm plant right at the bottom of the trunk and 2 more branches came poping out of that trunk so one set of leaves became 2 sets of leaves!
also it is possible to get the branch and make it to another tree but not alot of people i know had luck with woody branches but give it a try and put lots of root hormone powder that helps with root development
happy to help :)

this a monkey puzzle tree and yes, you can remove the second trunk if you like, but you won't be able to make it into another tree - the only way you could do that is to get a good portion of roots at the bottom, which might mean you kill off the other branch by disrupting the root system.

If that's another tree just behind it there really isn't room for the two of them. As Bamboo says Monkey Puzzles grow huge. Better decide which one you want to keep before they get any bigger!And I agree you can't root the branch you remove.