The imagery of the Refuge Tree, also referred to as Refuge Assembly, Refuge Field, Merit Field, Field of Merit or Field of Accumulation is a key part of a visualization and foundational meditation practice common to Tantric Buddhism. Based on descriptions in the liturgical texts of various traditions, Refuge Trees are often depicted in thangkas employed as objects of veneration, mnemonic devices and as a precursor to the contents being fully visualized by the Buddhist practitioner during the Refuge Formula or evocation.
While the concept of Refuge Trees appears in liturgical texts at least as early as the 16th century, based on known examples Refuge Tree paintings appear to have only become popular from the 18th century making them a late development in the history of Tibetan art.
The Refuge Tree is a symbol of the highest ideals of Buddhism, a traditional image in the Tibetan tradition that takes different forms in different schools. On the refuge tree are formal teachers and sages from Buddhism's history.
Source: WikipediaRefuge Tree Thangkas on this Website