avocado tree

Question

I haves black branches looks like its dying only a young tree the centre trunk and leaves are green

Answer 1

Black branches can be a sign that the tree has root rot. This disease of the roots is usually caused by overwatering or poorly-drained soil, which can lead to fungal infestations and other problems. Please see the following articles:
https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-pests-and-diseases.htm
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=1678