Russian investigators say that the tree hugger was perched some 50 ft above the ground.
The dead man was sitting on a branch of a pine tree in the northern outskirts of Tomsk, in Siberia.
It is believed that the unidentified man climbed the and died of hypothermia.
He was found with both arms hugging the tree.
The mummified body was spotted by local man Pavel Petrov, on 1 July, near a road leading to the 'closed city' of Seversk, from which foreigners are banned, where Russia enriches and reprocesses uranium and plutonium.
He told The Siberian Times: "It was me and my father who found the body. He was sitting on a pine tree some 50 metres away from the road.
"The rescuer who took the body off the tree said that most likely the man got so cold he decided to climb the tree, where he died from hypothermia."
The man was dressed in a navy vest, a sweatshirt, trousers and valenki - traditional Russian felt boots.
According to a preliminary examination by the Russian Investigative Committee, the man appears to have died about eight months ago .
The committee, in charge of major investigations in Russia, is seeking to identify the body.