To identify the tree we need close ups of the leaves and an indication of where in the world it is growing. My feeling at the moment is lilac but I wouldn’t bet on it since I can’t see any buds or tell clearly if the arrangement is alternate or opposite.

Oh, and you have bindweed at the base.

Appears to be a case of bacterial slime flux.

it looks like an old historic wound ... and the plant is probably rotting from the inside out.. and there is nothing to do about fixing that ... except removing it below the problem ...

and if you get the pix requested.. and we ID it ... we should be able to tell you how and if the plant will respond ...

so lets ID it ... ken

Lilac. These shrubs renew themselves from the root crown. Cut off the affected trunk and leave the rest of the stems, it will respond by producing new canes from the base.

cut it at 3 to 6 inches ... and run away ... lol ...

with no insult to a very old mature root mass ... it might fill that whole area in a year or two ...

but.. buds are on the plants now.. for next years spring show.. and the new stuff that grows next spring.. will not bloom...

and that is why you might leave some of the older trunks to bloom next year.. and then take them out afterwards ...

the pruning system is called rejuvenation pruning ...see link below

a good $10 folding tree saw.. or a TREE BLADE for a sawzall is well worth the investment ... lumber saws wont work well .... its the big teeth that remove wet wood that matters ....

https://www.walmart.com/ip/Hand-Pruning-Saw-Gardening-Tool-For-Home-Outdoor-Plants/185921589

https://duckduckgo.com/?q=sawzall+tree+saw+blade&t=ffsb&ia=products

ken

https://duckduckgo.com/?q=lilac+rejuvenation+pruning&t=ffcm&iax=videos&ia=videos