Red Bud tree
The brown interior is normal and is the heartwood of the tree. The disease most commonly found damaging redbuds is called verticillium wilt and it discolors the vascular tissue and this would show up as very dark areas in the growth rings. The heartwood on this plant is not showing dark streaking in either the heartwood or the white sapwood. From your picture I cannot see a disease problem. My redbud began to decline after last years record rainy period in May that left standing water that drained away too slowly. Root damage occurred due to lack of oxygen in the saturated soil. This was the first rainfall in over 25 years to saturate soils for an extended period in Washtenaw and surrounding counties. We are still seeing the damage from trees caused by the extended wet period in 2019. Redbuds are not long lived trees and 25 to 30 years is the common life span though in a site with good soil moisture, well draining soils, and protection from hot afternoon sun it can last much longer.