  Very recently, twisted graphene bilayer (TGB) around the first magic angle
1.1{\deg} has attracted much attention for the realization of exotic quantum
states, such as correlated insulator behavior and unconventional
superconductivity. Here we elaborately studied a series of TGBs around the
first magic angle engineered by heterostrain, where each layer is strained
independently. Our experiment indicated that a moderate heterostrain enables
the structural evolution from the small-angle TGB ( ~ 1.5{\deg}) to the
strained magic-angle TGB ({\theta} ~ 1.1{\deg}), exhibiting the characteristic
low-energy flat bands. The heterostrain can even drive the system into highly
strained tiny-angle TGBs ({\theta} << 1.1{\deg}) with large deformed tetragonal
superlattices, where a unique network of topological helical edge states
emerges. Furthermore, the predicted domain wall modes, which are strongly
localized and result in hexagon-triangle-mixed frustrated lattice derived from
Kagome lattice, are observed in the strained tiny-angle TGBs.
