const  mappedData = this.state.treeData
    .filter(data => data.title === "Category")
     .map(categ => {
      const { id, title, children, subtitle, type } = categ;

      function getChildren(children) {
        return children
          ? children.map(child => {
              if (child.title === "Item" || child.title === "Group") {
                const data = {
                  id: child.id,
                  name: child.subtitle,
                  type: child.type,
                  children: getChildren(child.children),
                  child_id: child.children
                    ? child.children.map(child => child.id)
                    : []
                };
                if (data.children.length === 0) delete data.children;
                if (data.child_id.length === 0) delete data.child_id;

                return data;
              } else {
                return {
                  id: child.id,
                  name: child.subtitle,
                  type: child.type
                };
              }
            })
          : [];
      }

      const data = {
        id: id,
        name: subtitle,
        type: type,
        children: getChildren(children),
        child_id: children ? children.map(child => child.id) : []
      };

      if (data.children.length === 0) delete data.children;
      if (data.child_id.length === 0) delete data.child_id;

      return data;
    });

<div className="json">
            <p> {JSON.stringify(mappedData)}</p>
</div>