A tribeam lets you attach a wide platform to a single tree trunk by widening the support base on the tree instead of attaching one beam to either side. Essentially, it’s an inverted truss with the flat beam on top and two 45 degree braces all locked together with notches and hardware. The required hardware and support can be found at https://www.treehousesupplies.com/Double_Knee_Brace_Bracket_p/br-dknee45.htm