<prompt> A Bone marrow transplant recipient patient developed chest infection. On HRCT Tree in bud appearance is seen. Most likely causative agent is -KlebsiellaPneumocystisTBRSV  <response>: The tree-in-bud sign is visible in high-resolution computed tomography HRCT and it is characterized by small centrilobular nodules of soft-tissue attenuation, connected to multiple branching linear structures of a similar caliber, originating from a single stalk.this is the main feature of pneumocystis jerovicii Ref Harrison20th edition pg 1079. 