Thank you for reaching out to Delaware Cooperative Extension! 

There are many factors that might affect the performance of your young Eastern redbud (Cercis canadensis) tree.

You did not indicate where you planted the tree. As this factsheet (link at bottom) from our Extension neighbors at Penn State mention, eastern redbuds prefer a mostly sunny location.  Some questions I have that would be helpful to know:
1. Do you know the variety or cultivar of the tree? If you purchased it, did it come with a tag?
2. Where on your property is it planted? What other structures or vegetation are nearby?
3. Did you take a soil test?  While eastern redbuds are tolerant within a range of pH, there may be other substances or lack of materials and nutrients in the soil of your chosen planting location. Link for soil tests at UD: https://www.udel.edu/academics/colleges/canr/cooperative-extension/environmental-stewardship/soil-testing/
4. Are there any signs of damage on the tree (holes, cracks, weeping, etc) especially at the base?
5. Is there mulch around the tree? If so, is mulch mounded up against the trunk? If so, pull the mulch away from the base.
6. The rounded-heart-shaped leaves on the tree are emerging now. Do the ones you have look healthy?
7. You indicate you live in Sussex. Is this tree exposed to coastal conditions? 

A few photographs would be helpful, one that captures the entire tree profile and some that are closeup showing the base and some of the productive and non-productive branches.

The first year of planting is a year of adjustment. A few years ago, we received a free Eastern Redbud from an organization in Delaware (I forget which one) and it was little more than a 24” stick with a few tiny branches at the top. It is now in its 4th year and for the first time, produced any of the noteworthy blossoms it is famous for. I suspect your tree was a bit larger. Our tree is now nearly 6 ft tall.  There is a saying in gardening, the first year it sleeps, the second year it creeps and the third year it leaps. In other words, it takes time for a new plant to adjust and acclimate to its surroundings. 

That being said, you do want to do a close inspection of the tree and rule out any injury, pests or disease, and you want to assure that the soil so crucial to its development is providing everything the tree needs. If not, there are remedies to amend your soil. 

Soil tests are available at your local Extension office. The photos would be helpful for agents and our plant diagnostician to perform a further analysis, see what factors might be stressing the tree and possible next steps. 

Extension fact sheet from Penn State Extension:
https://extension.psu.edu/eastern-redbud-a-superb-tree-for-almost-any-landscape

Hi, I would suggest you submit one or two of the struggling branch samples (finger width) to our diagnostic clinic, and we can check for disease. Submission instructions can be found here: udel.edu/extension/plantclinic

I would also suggest submitting a turf soil sample to our soil nutrition lab, as it may not be necessary to lime every year, depending on the soil PH and nutrients levels. Here are instructions: https://www.udel.edu/academics/colleges/canr/cooperative-extension/environmental-stewardship/soil-testing/