Betula nigra 'Little King' aka 'Fox Valley' may suit you well.

Dax

how small a garden???

ken

It's a 30' triangular space.

using dax suggestion.. and going to google images.. i say a grove of two trees will work in your 30 feet ...

i just cant fathom how you will do it.. with trees ...

i wonder if there are other things... that will LOOK like trees.. but be more suited to the very limited space ...

whats so special about the word GROVE???? ..memories??? ... poetry???

maybe if we can get to the root of the issue.. new ideas will spring to mind ...

maybe JMaples???

that 10 that pops up next to your name is rather confusing for someone from Chi town ....

ken

They don't have to be trees. I am envisioning smaller columnar architectural type trees, or bushes with interesting bark. I was thinking Coral Bark japanese maples, though they're not columnar.

thanks

Phyllostachys aureosulcata may suit you. I don't know much about root barriers but you could check into that.

Dax