After segmentation process for tree object, possibly you can make "density" as one of the feature spaces that used in the classification 

First you use an object based classification to identify individual trees. There are several ways to do that, depending on whether you work in forest with connected or interlaced tree crowns, or in savannah or urban areas, where individual trees and groups of trees are more common.

Once you have the individual trees, you calculate tree density either as number of individuals per unit area or as percentage of area covered by trees. You could do that by using a moving window in which you count the trees or the area covered by trees, or by using predefined units (e.g. tiles or adminitrative units) for which you could determine the cover percentage or the average number of individuals per hectare.

Use ecognation and its tutorial! It provides a wide range of object based classification operation. 

Dear manoj you can follow this link:

https://www.researchgate.net/post/Object_Based_Oriented_Image_Analysis_classification_in_ArcGIS_103?_tpcectx=profile_highlights